remove dependencies on contracts

Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>

src/api/dotnet/AST.cs

@@ -17,17 +17,16 @@ Notes:
 
 --*/
 
+using System.Diagnostics;
 using System;
 using System.Collections;
 using System.Collections.Generic;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
     /// <summary>
     /// The abstract syntax tree (AST) class.
     /// </summary>
-    [ContractVerification(true)]
     public class AST : Z3Object, IComparable
     {
         /// <summary>
@@ -114,8 +113,7 @@ namespace Microsoft.Z3
         /// <returns>A copy of the AST which is associated with <paramref name="ctx"/></returns>
         public AST Translate(Context ctx)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
-            Contract.Ensures(Contract.Result<AST>() != null);
 
             if (ReferenceEquals(Context, ctx))
                 return this;
@@ -202,14 +200,13 @@ namespace Microsoft.Z3
         /// </summary>
         public string SExpr()
         {
-            Contract.Ensures(Contract.Result<string>() != null);
 
             return Native.Z3_ast_to_string(Context.nCtx, NativeObject);
         }
 
         #region Internal
-        internal AST(Context ctx) : base(ctx) { Contract.Requires(ctx != null); }
+        internal AST(Context ctx) : base(ctx) { Debug.Assert(ctx != null); }
-        internal AST(Context ctx, IntPtr obj) : base(ctx, obj) { Contract.Requires(ctx != null); }
+        internal AST(Context ctx, IntPtr obj) : base(ctx, obj) { Debug.Assert(ctx != null); }
 
         internal class DecRefQueue : IDecRefQueue
         {
@@ -246,8 +243,7 @@ namespace Microsoft.Z3
 
         internal static AST Create(Context ctx, IntPtr obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
-            Contract.Ensures(Contract.Result<AST>() != null);
 
             switch ((Z3_ast_kind)Native.Z3_get_ast_kind(ctx.nCtx, obj))
             {

src/api/dotnet/ASTMap.cs

@@ -17,15 +17,14 @@ Notes:
     
 --*/
 
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
     /// <summary>
     /// Map from AST to AST
     /// </summary>
-    [ContractVerification(true)]
     internal class ASTMap : Z3Object
     {
         /// <summary>
@@ -35,7 +34,7 @@ namespace Microsoft.Z3
         /// <returns>True if <paramref name="k"/> is a key in the map, false otherwise.</returns>
         public bool Contains(AST k)
         {
-            Contract.Requires(k != null);
+            Debug.Assert(k != null);
 
             return 0 != Native.Z3_ast_map_contains(Context.nCtx, NativeObject, k.NativeObject);
         }
@@ -49,8 +48,7 @@ namespace Microsoft.Z3
         /// <param name="k">An AST</param>    
         public AST Find(AST k)
         {
-            Contract.Requires(k != null);
+            Debug.Assert(k != null);
-            Contract.Ensures(Contract.Result<AST>() != null);
 
             return new AST(Context, Native.Z3_ast_map_find(Context.nCtx, NativeObject, k.NativeObject));
         }
@@ -62,8 +60,8 @@ namespace Microsoft.Z3
         /// <param name="v">The value AST</param>
         public void Insert(AST k, AST v)
         {
-            Contract.Requires(k != null);
+            Debug.Assert(k != null);
-            Contract.Requires(v != null);
+            Debug.Assert(v != null);
 
             Native.Z3_ast_map_insert(Context.nCtx, NativeObject, k.NativeObject, v.NativeObject);
         }
@@ -74,7 +72,7 @@ namespace Microsoft.Z3
         /// <param name="k">An AST</param>
         public void Erase(AST k)
         {
-            Contract.Requires(k != null);
+            Debug.Assert(k != null);
 
             Native.Z3_ast_map_erase(Context.nCtx, NativeObject, k.NativeObject);
         }
@@ -119,12 +117,12 @@ namespace Microsoft.Z3
         internal ASTMap(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         internal ASTMap(Context ctx)
             : base(ctx, Native.Z3_mk_ast_map(ctx.nCtx))
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
 
         internal class DecRefQueue : IDecRefQueue

src/api/dotnet/ASTVector.cs

@@ -17,8 +17,8 @@ Notes:
     
 --*/
 
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
@@ -45,13 +45,12 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<AST>() != null);
 
                 return new AST(Context, Native.Z3_ast_vector_get(Context.nCtx, NativeObject, i));
             }
             set
             {
-                Contract.Requires(value != null);
+                Debug.Assert(value != null);
 
                 Native.Z3_ast_vector_set(Context.nCtx, NativeObject, i, value.NativeObject);
             }
@@ -73,7 +72,7 @@ namespace Microsoft.Z3
         /// <param name="a">An AST</param>
         public void Push(AST a)
         {
-            Contract.Requires(a != null);
+            Debug.Assert(a != null);
 
             Native.Z3_ast_vector_push(Context.nCtx, NativeObject, a.NativeObject);
         }
@@ -85,8 +84,7 @@ namespace Microsoft.Z3
         /// <returns>A new ASTVector</returns>
         public ASTVector Translate(Context ctx)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
-            Contract.Ensures(Contract.Result<ASTVector>() != null);
 
             return new ASTVector(Context, Native.Z3_ast_vector_translate(Context.nCtx, NativeObject, ctx.nCtx));
         }
@@ -232,8 +230,8 @@ namespace Microsoft.Z3
         }
 
         #region Internal
-        internal ASTVector(Context ctx, IntPtr obj) : base(ctx, obj) { Contract.Requires(ctx != null); }
+        internal ASTVector(Context ctx, IntPtr obj) : base(ctx, obj) { Debug.Assert(ctx != null); }
-        internal ASTVector(Context ctx) : base(ctx, Native.Z3_mk_ast_vector(ctx.nCtx)) { Contract.Requires(ctx != null); }
+        internal ASTVector(Context ctx) : base(ctx, Native.Z3_mk_ast_vector(ctx.nCtx)) { Debug.Assert(ctx != null); }
 
         internal class DecRefQueue : IDecRefQueue
         {

src/api/dotnet/AlgebraicNum.cs

@@ -16,8 +16,8 @@ Author:
 Notes:
     
 --*/
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
 
 #if !FRAMEWORK_LT_4
 using System.Numerics;
@@ -28,7 +28,6 @@ namespace Microsoft.Z3
     /// <summary>
     /// Algebraic numbers
     /// </summary>
-    [ContractVerification(true)]
     public class AlgebraicNum : ArithExpr
     {
         /// <summary>
@@ -40,7 +39,6 @@ namespace Microsoft.Z3
         /// <returns>A numeral Expr of sort Real</returns>
         public RatNum ToUpper(uint precision)
         {
-            Contract.Ensures(Contract.Result<RatNum>() != null);
 
             return new RatNum(Context, Native.Z3_get_algebraic_number_upper(Context.nCtx, NativeObject, precision));
         }
@@ -54,7 +52,6 @@ namespace Microsoft.Z3
         /// <returns>A numeral Expr of sort Real</returns>
         public RatNum ToLower(uint precision)
         {
-            Contract.Ensures(Contract.Result<RatNum>() != null);
 
             return new RatNum(Context, Native.Z3_get_algebraic_number_lower(Context.nCtx, NativeObject, precision));
         }
@@ -65,7 +62,6 @@ namespace Microsoft.Z3
         /// <remarks>The result has at most <paramref name="precision"/> decimal places.</remarks>    
         public string ToDecimal(uint precision)
         {
-            Contract.Ensures(Contract.Result<string>() != null);
 
             return Native.Z3_get_numeral_decimal_string(Context.nCtx, NativeObject, precision);
         }
@@ -74,7 +70,7 @@ namespace Microsoft.Z3
         internal AlgebraicNum(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         #endregion
     }

src/api/dotnet/ApplyResult.cs

@@ -17,8 +17,8 @@ Notes:
     
 --*/
 
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
@@ -26,7 +26,6 @@ namespace Microsoft.Z3
     /// ApplyResult objects represent the result of an application of a 
     /// tactic to a goal. It contains the subgoals that were produced.
     /// </summary>
-    [ContractVerification(true)]
     public class ApplyResult : Z3Object
     {
         /// <summary>
@@ -44,8 +43,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<Goal[]>() != null);
-                Contract.Ensures(Contract.Result<Goal[]>().Length == this.NumSubgoals);
 
                 uint n = NumSubgoals;
                 Goal[] res = new Goal[n];
@@ -67,7 +64,7 @@ namespace Microsoft.Z3
         internal ApplyResult(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
 
         internal class DecRefQueue : IDecRefQueue

src/api/dotnet/ArithExpr.cs

@@ -16,12 +16,12 @@ Author:
 Notes:
     
 --*/
+using System.Diagnostics;
 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
@@ -35,7 +35,7 @@ namespace Microsoft.Z3
         internal ArithExpr(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         #endregion
 

src/api/dotnet/ArithSort.cs

@@ -17,8 +17,8 @@ Notes:
     
 --*/
 
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
@@ -28,7 +28,7 @@ namespace Microsoft.Z3
     public class ArithSort : Sort
     {
         #region Internal
-        internal ArithSort(Context ctx, IntPtr obj) : base(ctx, obj) { Contract.Requires(ctx != null); }
+        internal ArithSort(Context ctx, IntPtr obj) : base(ctx, obj) { Debug.Assert(ctx != null); }
         #endregion
     };
 }

src/api/dotnet/ArrayExpr.cs

@@ -16,12 +16,12 @@ Author:
 Notes:
     
 --*/
+using System.Diagnostics;
 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
@@ -35,7 +35,7 @@ namespace Microsoft.Z3
         internal ArrayExpr(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         #endregion	
     }

src/api/dotnet/ArraySort.cs

@@ -17,15 +17,14 @@ Notes:
     
 --*/
 
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
     /// <summary>
     /// Array sorts.
     /// </summary>
-    [ContractVerification(true)]
     public class ArraySort : Sort
     {
         /// <summary>
@@ -35,7 +34,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<Sort>() != null);
 
                 return Sort.Create(Context, Native.Z3_get_array_sort_domain(Context.nCtx, NativeObject));
             }
@@ -48,27 +46,26 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<Sort>() != null);
 
                 return Sort.Create(Context, Native.Z3_get_array_sort_range(Context.nCtx, NativeObject));
             }
         }
 
         #region Internal
-        internal ArraySort(Context ctx, IntPtr obj) : base(ctx, obj) { Contract.Requires(ctx != null); }
+        internal ArraySort(Context ctx, IntPtr obj) : base(ctx, obj) { Debug.Assert(ctx != null); }
         internal ArraySort(Context ctx, Sort domain, Sort range)
             : base(ctx, Native.Z3_mk_array_sort(ctx.nCtx, domain.NativeObject, range.NativeObject))
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
-            Contract.Requires(domain != null);
+            Debug.Assert(domain != null);
-            Contract.Requires(range != null);
+            Debug.Assert(range != null);
         }
         internal ArraySort(Context ctx, Sort[] domain, Sort range)
             : base(ctx, Native.Z3_mk_array_sort_n(ctx.nCtx, (uint)domain.Length, AST.ArrayToNative(domain), range.NativeObject))
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
-            Contract.Requires(domain != null);
+            Debug.Assert(domain != null);
-            Contract.Requires(range != null);
+            Debug.Assert(range != null);
         }
         #endregion
     };

src/api/dotnet/BitVecExpr.cs

@@ -16,12 +16,12 @@ Author:
 Notes:
     
 --*/
+using System.Diagnostics;
 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
@@ -41,7 +41,7 @@ namespace Microsoft.Z3
 
         #region Internal
         /// <summary> Constructor for BitVecExpr </summary>
-        internal BitVecExpr(Context ctx, IntPtr obj) : base(ctx, obj) { Contract.Requires(ctx != null); }
+        internal BitVecExpr(Context ctx, IntPtr obj) : base(ctx, obj) { Debug.Assert(ctx != null); }
         #endregion
     }
 }

src/api/dotnet/BitVecNum.cs

@@ -16,8 +16,8 @@ Author:
 Notes:
     
 --*/
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
 
 #if !FRAMEWORK_LT_4
 using System.Numerics;
@@ -28,7 +28,6 @@ namespace Microsoft.Z3
     /// <summary>
     /// Bit-vector numerals
     /// </summary>
-    [ContractVerification(true)]
     public class BitVecNum : BitVecExpr
     {
         /// <summary>
@@ -109,7 +108,7 @@ namespace Microsoft.Z3
         }
 
         #region Internal
-        internal BitVecNum(Context ctx, IntPtr obj) : base(ctx, obj) { Contract.Requires(ctx != null); }
+        internal BitVecNum(Context ctx, IntPtr obj) : base(ctx, obj) { Debug.Assert(ctx != null); }
         #endregion
     }
 }

src/api/dotnet/BitVecSort.cs

@@ -17,8 +17,8 @@ Notes:
     
 --*/
 
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
@@ -36,7 +36,7 @@ namespace Microsoft.Z3
         }
 
         #region Internal
-        internal BitVecSort(Context ctx, IntPtr obj) : base(ctx, obj) { Contract.Requires(ctx != null); }
+        internal BitVecSort(Context ctx, IntPtr obj) : base(ctx, obj) { Debug.Assert(ctx != null); }
         #endregion
     };
 }

src/api/dotnet/BoolExpr.cs

@@ -16,12 +16,12 @@ Author:
 Notes:
     
 --*/
+using System.Diagnostics;
 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
@@ -32,7 +32,7 @@ namespace Microsoft.Z3
     {
         #region Internal
         /// <summary> Constructor for BoolExpr </summary>
-        internal BoolExpr(Context ctx, IntPtr obj) : base(ctx, obj) { Contract.Requires(ctx != null); }
+        internal BoolExpr(Context ctx, IntPtr obj) : base(ctx, obj) { Debug.Assert(ctx != null); }
         #endregion
 
         #region Operators

src/api/dotnet/BoolSort.cs

@@ -17,8 +17,8 @@ Notes:
     
 --*/
 
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
@@ -28,8 +28,8 @@ namespace Microsoft.Z3
     public class BoolSort : Sort
     {
         #region Internal
-        internal BoolSort(Context ctx, IntPtr obj) : base(ctx, obj) { Contract.Requires(ctx != null); }
+        internal BoolSort(Context ctx, IntPtr obj) : base(ctx, obj) { Debug.Assert(ctx != null); }
-        internal BoolSort(Context ctx) : base(ctx, Native.Z3_mk_bool_sort(ctx.nCtx)) { Contract.Requires(ctx != null); }
+        internal BoolSort(Context ctx) : base(ctx, Native.Z3_mk_bool_sort(ctx.nCtx)) { Debug.Assert(ctx != null); }
         #endregion
     };
 }

src/api/dotnet/Constructor.cs

@@ -17,15 +17,14 @@ Notes:
     
 --*/
 
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
     /// <summary>
     /// Constructors are used for datatype sorts.
     /// </summary>
-    [ContractVerification(true)]
     public class Constructor : Z3Object
     {
         /// <summary>
@@ -46,7 +45,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<FuncDecl>() != null);
                 IntPtr constructor = IntPtr.Zero;
                 IntPtr tester = IntPtr.Zero;
                 IntPtr[] accessors = new IntPtr[n];
@@ -62,7 +60,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<FuncDecl>() != null);
                 IntPtr constructor = IntPtr.Zero;
                 IntPtr tester = IntPtr.Zero;
                 IntPtr[] accessors = new IntPtr[n];
@@ -78,7 +75,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<FuncDecl[]>() != null);
                 IntPtr constructor = IntPtr.Zero;
                 IntPtr tester = IntPtr.Zero;
                 IntPtr[] accessors = new IntPtr[n];
@@ -105,9 +101,9 @@ namespace Microsoft.Z3
                              Sort[] sorts, uint[] sortRefs)
             : base(ctx)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
-            Contract.Requires(name != null);
+            Debug.Assert(name != null);
-            Contract.Requires(recognizer != null);
+            Debug.Assert(recognizer != null);
 
             n = AST.ArrayLength(fieldNames);
 

src/api/dotnet/ConstructorList.cs

@@ -17,12 +17,12 @@ Notes:
     
 --*/
 
+using System.Diagnostics;
 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
@@ -43,14 +43,14 @@ namespace Microsoft.Z3
         internal ConstructorList(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
 
         internal ConstructorList(Context ctx, Constructor[] constructors)
             : base(ctx)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
-            Contract.Requires(constructors != null);
+            Debug.Assert(constructors != null);
 
             NativeObject = Native.Z3_mk_constructor_list(Context.nCtx, (uint)constructors.Length, Constructor.ArrayToNative(constructors));
         }

src/api/dotnet/DatatypeExpr.cs

@@ -16,12 +16,12 @@ Author:
 Notes:
     
 --*/
+using System.Diagnostics;
 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
@@ -35,7 +35,7 @@ namespace Microsoft.Z3
         internal DatatypeExpr(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         #endregion
     }

src/api/dotnet/DatatypeSort.cs

@@ -17,15 +17,14 @@ Notes:
     
 --*/
 
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
     /// <summary>
     /// Datatype sorts.
     /// </summary>
-    [ContractVerification(true)]
     public class DatatypeSort : Sort
     {
         /// <summary>
@@ -43,7 +42,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<FuncDecl[]>() != null);
 
                 uint n = NumConstructors;
                 FuncDecl[] res = new FuncDecl[n];
@@ -60,7 +58,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<FuncDecl[]>() != null);
 
                 uint n = NumConstructors;
                 FuncDecl[] res = new FuncDecl[n];
@@ -77,7 +74,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<FuncDecl[][]>() != null);
 
                 uint n = NumConstructors;
                 FuncDecl[][] res = new FuncDecl[n][];
@@ -95,14 +91,14 @@ namespace Microsoft.Z3
         }
 
         #region Internal
-        internal DatatypeSort(Context ctx, IntPtr obj) : base(ctx, obj) { Contract.Requires(ctx != null); }
+        internal DatatypeSort(Context ctx, IntPtr obj) : base(ctx, obj) { Debug.Assert(ctx != null); }
 
         internal DatatypeSort(Context ctx, Symbol name, Constructor[] constructors)
             : base(ctx, Native.Z3_mk_datatype(ctx.nCtx, name.NativeObject, (uint)constructors.Length, ArrayToNative(constructors)))
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
-            Contract.Requires(name != null);
+            Debug.Assert(name != null);
-            Contract.Requires(constructors != null);
+            Debug.Assert(constructors != null);
         }
         #endregion
     };

src/api/dotnet/Deprecated.cs

@@ -17,17 +17,16 @@ Author:
 Notes:
     
 --*/
+using System.Diagnostics;
 using System;
 using System.Collections.Generic;
 using System.Runtime.InteropServices;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
     /// <summary>
     /// The main interaction with Z3 happens via the Context.
     /// </summary>
-    [ContractVerification(true)]
     public class Deprecated 
     {
 

src/api/dotnet/EnumSort.cs

@@ -17,15 +17,14 @@ Notes:
     
 --*/
 
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
     /// <summary>
     /// Enumeration sorts.
     /// </summary>
-    [ContractVerification(true)]
     public class EnumSort : Sort
     {
         /// <summary>
@@ -35,7 +34,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<FuncDecl[]>() != null);
                 uint n = Native.Z3_get_datatype_sort_num_constructors(Context.nCtx, NativeObject);
                 FuncDecl[] t = new FuncDecl[n];
                 for (uint i = 0; i < n; i++)
@@ -61,7 +59,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<Expr[]>() != null);
                 FuncDecl[] cds = ConstDecls;
                 Expr[] t = new Expr[cds.Length];
                 for (uint i = 0; i < t.Length; i++)
@@ -87,7 +84,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<FuncDecl[]>() != null);
                 uint n = Native.Z3_get_datatype_sort_num_constructors(Context.nCtx, NativeObject);
                 FuncDecl[] t = new FuncDecl[n];
                 for (uint i = 0; i < n; i++)
@@ -110,9 +106,9 @@ namespace Microsoft.Z3
         internal EnumSort(Context ctx, Symbol name, Symbol[] enumNames)
             : base(ctx, IntPtr.Zero)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
-            Contract.Requires(name != null);
+            Debug.Assert(name != null);
-            Contract.Requires(enumNames != null);
+            Debug.Assert(enumNames != null);
 
             int n = enumNames.Length;
             IntPtr[] n_constdecls = new IntPtr[n];

src/api/dotnet/Expr.cs

@@ -17,15 +17,16 @@ Notes:
 
 --*/
 
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
+using System.Linq;
+
 
 namespace Microsoft.Z3
 {
     /// <summary>
     /// Expressions are terms.
     /// </summary>
-    [ContractVerification(true)]
     public class Expr : AST
     {
         /// <summary>
@@ -35,7 +36,6 @@ namespace Microsoft.Z3
         /// <seealso cref="Context.SimplifyHelp"/>
         public Expr Simplify(Params p = null)
         {
-            Contract.Ensures(Contract.Result<Expr>() != null);
 
             if (p == null)
                 return Expr.Create(Context, Native.Z3_simplify(Context.nCtx, NativeObject));
@@ -50,7 +50,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<FuncDecl>() != null);
                 return new FuncDecl(Context, Native.Z3_get_app_decl(Context.nCtx, NativeObject));
             }
         }
@@ -79,7 +78,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<Expr[]>() != null);
 
                 uint n = NumArgs;
                 Expr[] res = new Expr[n];
@@ -94,7 +92,6 @@ namespace Microsoft.Z3
         /// </summary>
         public Expr Arg(uint i)
         {
-            Contract.Ensures(Contract.Result<Expr>() != null);
             return Expr.Create(Context, Native.Z3_get_app_arg(Context.nCtx, NativeObject, i));
         }
 
@@ -104,8 +101,8 @@ namespace Microsoft.Z3
         /// </summary>
         public void Update(Expr[] args)
         {
-            Contract.Requires(args != null);
+            Debug.Assert(args != null);
-            Contract.Requires(Contract.ForAll(args, a => a != null));
+            Debug.Assert(args.All(a => a != null));
 
             Context.CheckContextMatch<Expr>(args);
             if (IsApp && args.Length != NumArgs)
@@ -123,11 +120,10 @@ namespace Microsoft.Z3
         /// </remarks>
         public Expr Substitute(Expr[] from, Expr[] to)
         {
-            Contract.Requires(from != null);
+            Debug.Assert(from != null);
-            Contract.Requires(to != null);
+            Debug.Assert(to != null);
-            Contract.Requires(Contract.ForAll(from, f => f != null));
+            Debug.Assert(from.All(f => f != null));
-            Contract.Requires(Contract.ForAll(to, t => t != null));
+            Debug.Assert(to.All(t => t != null));
-            Contract.Ensures(Contract.Result<Expr>() != null);
 
             Context.CheckContextMatch<Expr>(from);
             Context.CheckContextMatch<Expr>(to);
@@ -142,9 +138,8 @@ namespace Microsoft.Z3
         /// <seealso cref="Substitute(Expr[],Expr[])"/>
         public Expr Substitute(Expr from, Expr to)
         {
-            Contract.Requires(from != null);
+            Debug.Assert(from != null);
-            Contract.Requires(to != null);
+            Debug.Assert(to != null);
-            Contract.Ensures(Contract.Result<Expr>() != null);
 
             return Substitute(new Expr[] { from }, new Expr[] { to });
         }
@@ -157,9 +152,8 @@ namespace Microsoft.Z3
         /// </remarks>
         public Expr SubstituteVars(Expr[] to)
         {
-            Contract.Requires(to != null);
+            Debug.Assert(to != null);
-            Contract.Requires(Contract.ForAll(to, t => t != null));
+            Debug.Assert(to.All(t => t != null));
-            Contract.Ensures(Contract.Result<Expr>() != null);
 
             Context.CheckContextMatch<Expr>(to);
             return Expr.Create(Context, Native.Z3_substitute_vars(Context.nCtx, NativeObject, (uint)to.Length, Expr.ArrayToNative(to)));
@@ -207,7 +201,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<Sort>() != null);
                 return Sort.Create(Context, Native.Z3_get_sort(Context.nCtx, NativeObject));
             }
         }
@@ -332,7 +325,7 @@ namespace Microsoft.Z3
         /// <summary>
         /// Retrieve bound of at-most
         /// </summary>
-        public uint AtMostBound { get { Contract.Requires(IsAtMost); return (uint)FuncDecl.Parameters[0].Int; } }
+        public uint AtMostBound { get { Debug.Assert(IsAtMost); return (uint)FuncDecl.Parameters[0].Int; } }
 
         /// <summary>
         /// Indicates whether the term is at-least
@@ -342,7 +335,7 @@ namespace Microsoft.Z3
         /// <summary>
         /// Retrieve bound of at-least
         /// </summary>
-        public uint AtLeastBound { get { Contract.Requires(IsAtLeast); return (uint)FuncDecl.Parameters[0].Int; } }
+        public uint AtLeastBound { get { Debug.Assert(IsAtLeast); return (uint)FuncDecl.Parameters[0].Int; } }
 
         /// <summary>
         /// Indicates whether the term is pbeq
@@ -1816,8 +1809,6 @@ namespace Microsoft.Z3
                 if (!IsVar)
                     throw new Z3Exception("Term is not a bound variable.");
 
-                Contract.EndContractBlock();
-
                 return Native.Z3_get_index_value(Context.nCtx, NativeObject);
             }
         }
@@ -1827,10 +1818,9 @@ namespace Microsoft.Z3
         /// <summary>
         /// Constructor for Expr
         /// </summary>
-        internal protected Expr(Context ctx, IntPtr obj) : base(ctx, obj) { Contract.Requires(ctx != null); }
+        internal protected Expr(Context ctx, IntPtr obj) : base(ctx, obj) { Debug.Assert(ctx != null); }
 
 #if DEBUG
-        [Pure]
         internal override void CheckNativeObject(IntPtr obj)
         {
             if (Native.Z3_is_app(Context.nCtx, obj) == 0 &&
@@ -1841,12 +1831,10 @@ namespace Microsoft.Z3
         }
 #endif
 
-        [Pure]
         internal static Expr Create(Context ctx, FuncDecl f, params Expr[] arguments)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
-            Contract.Requires(f != null);
+            Debug.Assert(f != null);
-            Contract.Ensures(Contract.Result<Expr>() != null);
 
             IntPtr obj = Native.Z3_mk_app(ctx.nCtx, f.NativeObject,
                                           AST.ArrayLength(arguments),
@@ -1854,11 +1842,9 @@ namespace Microsoft.Z3
             return Create(ctx, obj);
         }
 
-        [Pure]
         new internal static Expr Create(Context ctx, IntPtr obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
-            Contract.Ensures(Contract.Result<Expr>() != null);
 
             Z3_ast_kind k = (Z3_ast_kind)Native.Z3_get_ast_kind(ctx.nCtx, obj);
             if (k == Z3_ast_kind.Z3_QUANTIFIER_AST)

src/api/dotnet/FPExpr.cs

@@ -16,12 +16,12 @@ Author:
 Notes:
     
 --*/
+using System.Diagnostics;
 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {    
@@ -45,7 +45,7 @@ namespace Microsoft.Z3
         internal FPExpr(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         #endregion
     }

src/api/dotnet/FPNum.cs

@@ -16,15 +16,14 @@ Author:
 Notes:
 
 --*/
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
     /// <summary>
     /// FloatiungPoint Numerals
     /// </summary>
-    [ContractVerification(true)]
     public class FPNum : FPExpr
     {
         /// <summary>
@@ -175,7 +174,7 @@ namespace Microsoft.Z3
         internal FPNum(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         #endregion
 

src/api/dotnet/FPRMExpr.cs

@@ -16,12 +16,12 @@ Author:
 Notes:
     
 --*/
+using System.Diagnostics;
 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
@@ -35,7 +35,7 @@ namespace Microsoft.Z3
         internal FPRMExpr(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         #endregion
     }

src/api/dotnet/FPRMNum.cs

@@ -16,12 +16,12 @@ Author:
 Notes:
     
 --*/
+using System.Diagnostics;
 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
@@ -93,7 +93,7 @@ namespace Microsoft.Z3
         internal FPRMNum(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         #endregion
     }

src/api/dotnet/FPRMSort.cs

@@ -17,8 +17,8 @@ Notes:
     
 --*/
 
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
@@ -31,12 +31,12 @@ namespace Microsoft.Z3
         internal FPRMSort(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         internal FPRMSort(Context ctx)
             : base(ctx, Native.Z3_mk_fpa_rounding_mode_sort(ctx.nCtx))
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         #endregion
     }

src/api/dotnet/FPSort.cs

@@ -16,8 +16,8 @@ Author:
 Notes:
     
 --*/
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
@@ -40,12 +40,12 @@ namespace Microsoft.Z3
         internal FPSort(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         internal FPSort(Context ctx, uint ebits, uint sbits)
             : base(ctx, Native.Z3_mk_fpa_sort(ctx.nCtx, ebits, sbits))
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         #endregion
     }    

src/api/dotnet/FiniteDomainExpr.cs

@@ -16,8 +16,8 @@ Author:
 Notes:
 
 --*/
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
@@ -31,7 +31,7 @@ namespace Microsoft.Z3
         internal FiniteDomainExpr(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         #endregion
     }

src/api/dotnet/FiniteDomainNum.cs

@@ -16,8 +16,8 @@ Author:
 Notes:
 
 --*/
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
 
 #if !FRAMEWORK_LT_4
 using System.Numerics;
@@ -28,7 +28,6 @@ namespace Microsoft.Z3
     /// <summary>
     /// Finite-domain numerals
     /// </summary>
-    [ContractVerification(true)]
     public class FiniteDomainNum : FiniteDomainExpr
     {
         /// <summary>
@@ -109,7 +108,7 @@ namespace Microsoft.Z3
         }
 
         #region Internal
-        internal FiniteDomainNum(Context ctx, IntPtr obj) : base(ctx, obj) { Contract.Requires(ctx != null); }
+        internal FiniteDomainNum(Context ctx, IntPtr obj) : base(ctx, obj) { Debug.Assert(ctx != null); }
         #endregion
     }
 }

src/api/dotnet/FiniteDomainSort.cs

@@ -17,15 +17,14 @@ Notes:
     
 --*/
 
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
     /// <summary>
     /// Finite domain sorts.
     /// </summary>
-    [ContractVerification(true)]
     public class FiniteDomainSort : Sort
     {
         /// <summary>
@@ -45,13 +44,13 @@ namespace Microsoft.Z3
         internal FiniteDomainSort(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         internal FiniteDomainSort(Context ctx, Symbol name, ulong size)
             : base(ctx, Native.Z3_mk_finite_domain_sort(ctx.nCtx, name.NativeObject, size))
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
-            Contract.Requires(name != null);
+            Debug.Assert(name != null);
 
         }
         #endregion

src/api/dotnet/Fixedpoint.cs

@@ -18,14 +18,14 @@ Notes:
 --*/
 
 using System;
-using System.Diagnostics.Contracts;
+using System.Diagnostics;
+using System.Linq;
 
 namespace Microsoft.Z3
 {
     /// <summary>
     /// Object for managing fixedpoints
     /// </summary>
-    [ContractVerification(true)]
     public class Fixedpoint : Z3Object
     {
 
@@ -36,7 +36,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<string>() != null);
                 return Native.Z3_fixedpoint_get_help(Context.nCtx, NativeObject);
             }
         }
@@ -48,7 +47,7 @@ namespace Microsoft.Z3
         {
             set
             {
-                Contract.Requires(value != null);
+                Debug.Assert(value != null);
                 Context.CheckContextMatch(value);
                 Native.Z3_fixedpoint_set_params(Context.nCtx, NativeObject, value.NativeObject);
             }
@@ -68,8 +67,8 @@ namespace Microsoft.Z3
         /// </summary>        
         public void Assert(params BoolExpr[] constraints)
         {
-            Contract.Requires(constraints != null);
+            Debug.Assert(constraints != null);
-            Contract.Requires(Contract.ForAll(constraints, c => c != null));
+            Debug.Assert(constraints.All(c => c != null));
 
             Context.CheckContextMatch<BoolExpr>(constraints);
             foreach (BoolExpr a in constraints)
@@ -91,7 +90,7 @@ namespace Microsoft.Z3
         /// </summary>       
         public void RegisterRelation(FuncDecl f)
         {
-            Contract.Requires(f != null);
+            Debug.Assert(f != null);
 
             Context.CheckContextMatch(f);
             Native.Z3_fixedpoint_register_relation(Context.nCtx, NativeObject, f.NativeObject);
@@ -102,7 +101,7 @@ namespace Microsoft.Z3
         /// </summary>        
         public void AddRule(BoolExpr rule, Symbol name = null)
         {
-            Contract.Requires(rule != null);
+            Debug.Assert(rule != null);
 
             Context.CheckContextMatch(rule);
             Native.Z3_fixedpoint_add_rule(Context.nCtx, NativeObject, rule.NativeObject, AST.GetNativeObject(name));
@@ -113,8 +112,8 @@ namespace Microsoft.Z3
         /// </summary>        
         public void AddFact(FuncDecl pred, params uint[] args)
         {
-            Contract.Requires(pred != null);
+            Debug.Assert(pred != null);
-            Contract.Requires(args != null);
+            Debug.Assert(args != null);
 
             Context.CheckContextMatch(pred);
             Native.Z3_fixedpoint_add_fact(Context.nCtx, NativeObject, pred.NativeObject, (uint)args.Length, args);
@@ -128,7 +127,7 @@ namespace Microsoft.Z3
         /// </summary>        
         public Status Query(BoolExpr query)
         {
-            Contract.Requires(query != null);
+            Debug.Assert(query != null);
 
             Context.CheckContextMatch(query);
             Z3_lbool r = (Z3_lbool)Native.Z3_fixedpoint_query(Context.nCtx, NativeObject, query.NativeObject);
@@ -148,8 +147,8 @@ namespace Microsoft.Z3
         /// </summary>        
         public Status Query(params FuncDecl[] relations)
         {
-            Contract.Requires(relations != null);
+            Debug.Assert(relations != null);
-            Contract.Requires(Contract.ForAll(0, relations.Length, i => relations[i] != null));
+            Debug.Assert(relations.All(rel => rel != null));
 
             Context.CheckContextMatch<FuncDecl>(relations);
             Z3_lbool r = (Z3_lbool)Native.Z3_fixedpoint_query_relations(Context.nCtx, NativeObject,
@@ -187,7 +186,7 @@ namespace Microsoft.Z3
         /// </summary>        
         public void UpdateRule(BoolExpr rule, Symbol name)
         {
-            Contract.Requires(rule != null);
+            Debug.Assert(rule != null);
 
             Context.CheckContextMatch(rule);
             Native.Z3_fixedpoint_update_rule(Context.nCtx, NativeObject, rule.NativeObject, AST.GetNativeObject(name));
@@ -208,7 +207,6 @@ namespace Microsoft.Z3
         /// </summary>                
         public string GetReasonUnknown()
         {
-            Contract.Ensures(Contract.Result<string>() != null);
 
             return Native.Z3_fixedpoint_get_reason_unknown(Context.nCtx, NativeObject);
         }
@@ -252,7 +250,7 @@ namespace Microsoft.Z3
         /// </summary>                
         public void SetPredicateRepresentation(FuncDecl f, Symbol[] kinds)
         {
-            Contract.Requires(f != null);
+            Debug.Assert(f != null);
 
             Native.Z3_fixedpoint_set_predicate_representation(Context.nCtx, NativeObject,
                                f.NativeObject, AST.ArrayLength(kinds), Symbol.ArrayToNative(kinds));
@@ -276,7 +274,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<BoolExpr[]>() != null);
 
                 ASTVector av = new ASTVector(Context, Native.Z3_fixedpoint_get_rules(Context.nCtx, NativeObject));
                 return av.ToBoolExprArray();
@@ -290,7 +287,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<BoolExpr[]>() != null);
 
                 ASTVector av = new ASTVector(Context, Native.Z3_fixedpoint_get_assertions(Context.nCtx, NativeObject));
                 return av.ToBoolExprArray();
@@ -304,7 +300,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<Statistics>() != null);
 
                 return new Statistics(Context, Native.Z3_fixedpoint_get_statistics(Context.nCtx, NativeObject));
             }
@@ -335,12 +330,12 @@ namespace Microsoft.Z3
         internal Fixedpoint(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         internal Fixedpoint(Context ctx)
             : base(ctx, Native.Z3_mk_fixedpoint(ctx.nCtx))
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
 
         internal class DecRefQueue : IDecRefQueue

src/api/dotnet/FuncDecl.cs

@@ -18,14 +18,15 @@ Notes:
 --*/
 
 using System;
-using System.Diagnostics.Contracts;
+using System.Diagnostics;
+using System.Linq;
+
 
 namespace Microsoft.Z3
 {
     /// <summary>
     /// Function declarations.
     /// </summary>
-    [ContractVerification(true)]
     public class FuncDecl : AST
     {
         /// <summary>
@@ -108,7 +109,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<Sort[]>() != null);
 
                 uint n = DomainSize;
 
@@ -126,7 +126,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<Sort>() != null);
                 return Sort.Create(Context, Native.Z3_get_range(Context.nCtx, NativeObject));
             }
         }
@@ -146,7 +145,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<Symbol>() != null);
                 return Symbol.Create(Context, Native.Z3_get_decl_name(Context.nCtx, NativeObject));
             }
         }
@@ -166,7 +164,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<Parameter[]>() != null);
 
                 uint num = NumParameters;
                 Parameter[] res = new Parameter[num];
@@ -287,22 +284,22 @@ namespace Microsoft.Z3
         internal FuncDecl(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
 
         internal FuncDecl(Context ctx, Symbol name, Sort[] domain, Sort range)
             : base(ctx, Native.Z3_mk_func_decl(ctx.nCtx, name.NativeObject, AST.ArrayLength(domain), AST.ArrayToNative(domain), range.NativeObject))
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
-            Contract.Requires(name != null);
+            Debug.Assert(name != null);
-            Contract.Requires(range != null);
+            Debug.Assert(range != null);
         }
 
         internal FuncDecl(Context ctx, string prefix, Sort[] domain, Sort range)
             : base(ctx, Native.Z3_mk_fresh_func_decl(ctx.nCtx, prefix, AST.ArrayLength(domain), AST.ArrayToNative(domain), range.NativeObject))
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
-            Contract.Requires(range != null);
+            Debug.Assert(range != null);
         }
 
 #if DEBUG
@@ -335,7 +332,7 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Requires(args == null || Contract.ForAll(args, a => a != null));
+                Debug.Assert(args == null || args.All(a => a != null));
 
                 return Apply(args);
             }
@@ -348,7 +345,7 @@ namespace Microsoft.Z3
         /// <returns></returns>
         public Expr Apply(params Expr[] args)
         {
-            Contract.Requires(args == null || Contract.ForAll(args, a => a != null));
+            Debug.Assert(args == null || args.All(a => a != null));
 
             Context.CheckContextMatch<Expr>(args);
             return Expr.Create(Context, this, args);

src/api/dotnet/FuncInterp.cs

@@ -17,8 +17,8 @@ Notes:
     
 --*/
 
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
@@ -26,7 +26,6 @@ namespace Microsoft.Z3
     ///  A function interpretation is represented as a finite map and an 'else' value.
     ///  Each entry in the finite map represents the value of a function given a set of arguments.  
     /// </summary>
-    [ContractVerification(true)]
     public class FuncInterp : Z3Object
     {
         /// <summary>
@@ -42,7 +41,6 @@ namespace Microsoft.Z3
             {
                 get
                 {
-                    Contract.Ensures(Contract.Result<Expr>() != null);
                     return Expr.Create(Context, Native.Z3_func_entry_get_value(Context.nCtx, NativeObject));
                 }
             }
@@ -62,8 +60,6 @@ namespace Microsoft.Z3
             {
                 get
                 {
-                    Contract.Ensures(Contract.Result<Expr[]>() != null);
-                    Contract.Ensures(Contract.Result<Expr[]>().Length == this.NumArgs);
 
                     uint n = NumArgs;
                     Expr[] res = new Expr[n];
@@ -87,7 +83,7 @@ namespace Microsoft.Z3
             }
 
             #region Internal
-            internal Entry(Context ctx, IntPtr obj) : base(ctx, obj) { Contract.Requires(ctx != null); }
+            internal Entry(Context ctx, IntPtr obj) : base(ctx, obj) { Debug.Assert(ctx != null); }
 
             internal class DecRefQueue : IDecRefQueue
             {
@@ -133,8 +129,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<Entry[]>() != null);
-                Contract.Ensures(Contract.ForAll(0, Contract.Result<Entry[]>().Length, j => Contract.Result<Entry[]>()[j] != null));
 
                 uint n = NumEntries;
                 Entry[] res = new Entry[n];
@@ -151,7 +145,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<Expr>() != null);
 
                 return Expr.Create(Context, Native.Z3_func_interp_get_else(Context.nCtx, NativeObject));
             }
@@ -194,7 +187,7 @@ namespace Microsoft.Z3
         internal FuncInterp(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
 
         internal class DecRefQueue : IDecRefQueue

src/api/dotnet/Global.cs

@@ -17,9 +17,9 @@ Notes:
     
 --*/
 
+using System.Diagnostics;
 using System;
 using System.Runtime.InteropServices;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {

src/api/dotnet/Goal.cs

@@ -18,7 +18,8 @@ Notes:
 --*/
 
 using System;
-using System.Diagnostics.Contracts;
+using System.Diagnostics;
+using System.Linq;
 
 namespace Microsoft.Z3
 {
@@ -27,7 +28,6 @@ namespace Microsoft.Z3
     /// of formulas, that can be solved and/or transformed using
     /// tactics and solvers.
     /// </summary>
-    [ContractVerification(true)]
     public class Goal : Z3Object
     {
         /// <summary>
@@ -79,13 +79,13 @@ namespace Microsoft.Z3
         /// </summary>   
         public void Assert(params BoolExpr[] constraints)
         {
-            Contract.Requires(constraints != null);
+            Debug.Assert(constraints != null);
-            Contract.Requires(Contract.ForAll(constraints, c => c != null));
+            Debug.Assert(constraints.All(c => c != null));
 
             Context.CheckContextMatch<BoolExpr>(constraints);
             foreach (BoolExpr c in constraints)
             {
-                Contract.Assert(c != null); // It was an assume, now made an assert just to be sure we do not regress
+                Debug.Assert(c != null); // It was an assume, now made an assert just to be sure we do not regress
                 Native.Z3_goal_assert(Context.nCtx, NativeObject, c.NativeObject);
             }
         }
@@ -140,7 +140,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<BoolExpr[]>() != null);
 
                 uint n = Size;
                 BoolExpr[] res = new BoolExpr[n];
@@ -181,7 +180,6 @@ namespace Microsoft.Z3
         /// <returns>A model for <c>g</c></returns>
         public Model ConvertModel(Model m)
         {
-            Contract.Ensures(Contract.Result<Model>() != null);
             if (m != null)
                return new Model(Context, Native.Z3_goal_convert_model(Context.nCtx, NativeObject, m.NativeObject));
             else
@@ -194,7 +192,7 @@ namespace Microsoft.Z3
         /// </summary>
         public Goal Translate(Context ctx)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
 
             return new Goal(ctx, Native.Z3_goal_translate(Context.nCtx, NativeObject, ctx.nCtx));
         }
@@ -248,12 +246,12 @@ namespace Microsoft.Z3
         }
 
         #region Internal
-        internal Goal(Context ctx, IntPtr obj) : base(ctx, obj) { Contract.Requires(ctx != null); }
+        internal Goal(Context ctx, IntPtr obj) : base(ctx, obj) { Debug.Assert(ctx != null); }
 
         internal Goal(Context ctx, bool models, bool unsatCores, bool proofs)
             : base(ctx, Native.Z3_mk_goal(ctx.nCtx, (byte)(models ? 1 : 0), (byte)(unsatCores ? 1 : 0), (byte)(proofs ? 1 : 0)))
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
 
         internal class DecRefQueue : IDecRefQueue

src/api/dotnet/IDecRefQueue.cs

@@ -17,26 +17,24 @@ Notes:
     
 --*/
 
+using System.Diagnostics;
 using System;
 using System.Collections;
 using System.Collections.Generic;
 using System.Threading;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
     /// <summary>
     /// DecRefQueue interface
     /// </summary>
-    [ContractClass(typeof(DecRefQueueContracts))]
     public abstract class IDecRefQueue
     {
         #region Object invariant
 
-        [ContractInvariantMethod]
         private void ObjectInvariant()
         {
-            Contract.Invariant(this.m_queue != null);
+            Debug.Assert(this.m_queue != null);
         }
 
         #endregion
@@ -61,7 +59,7 @@ namespace Microsoft.Z3
 
         internal void IncAndClear(Context ctx, IntPtr o)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
 
             IncRef(ctx, o);
             if (m_queue.Count >= m_move_limit) Clear(ctx);
@@ -79,7 +77,7 @@ namespace Microsoft.Z3
 
         internal void Clear(Context ctx)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
 
             lock (m_lock)
             {
@@ -90,17 +88,16 @@ namespace Microsoft.Z3
         }
     }
 
-    [ContractClassFor(typeof(IDecRefQueue))]
     abstract class DecRefQueueContracts : IDecRefQueue
     {
         internal override void IncRef(Context ctx, IntPtr obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
 
         internal override void DecRef(Context ctx, IntPtr obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
     }
 }

src/api/dotnet/IntExpr.cs

@@ -16,12 +16,12 @@ Author:
 Notes:
     
 --*/
+using System.Diagnostics;
 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
@@ -35,7 +35,7 @@ namespace Microsoft.Z3
         internal IntExpr(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         #endregion
     }

src/api/dotnet/IntNum.cs

@@ -16,8 +16,8 @@ Author:
 Notes:
     
 --*/
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
 
 #if !FRAMEWORK_LT_4
 using System.Numerics;
@@ -28,7 +28,6 @@ namespace Microsoft.Z3
     /// <summary>
     /// Integer Numerals
     /// </summary>
-    [ContractVerification(true)]
     public class IntNum : IntExpr
     {
 
@@ -36,7 +35,7 @@ namespace Microsoft.Z3
         internal IntNum(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         #endregion
 

src/api/dotnet/IntSort.cs

@@ -17,8 +17,8 @@ Notes:
     
 --*/
 
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
@@ -31,12 +31,12 @@ namespace Microsoft.Z3
         internal IntSort(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         internal IntSort(Context ctx)
             : base(ctx, Native.Z3_mk_int_sort(ctx.nCtx))
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         #endregion
     }

src/api/dotnet/IntSymbol.cs

@@ -18,15 +18,14 @@ Notes:
 --*/
 
 using System;
+using System.Diagnostics;
 using System.Runtime.InteropServices;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
     /// <summary>
     /// Numbered symbols
     /// </summary>
-    [ContractVerification(true)]
     public class IntSymbol : Symbol
     {
         /// <summary>
@@ -47,12 +46,12 @@ namespace Microsoft.Z3
         internal IntSymbol(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         internal IntSymbol(Context ctx, int i)
             : base(ctx, Native.Z3_mk_int_symbol(ctx.nCtx, i))
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
 
 #if DEBUG

src/api/dotnet/Lambda.cs

@@ -18,14 +18,14 @@ Notes:
 --*/
 
 using System;
-using System.Diagnostics.Contracts;
+using System.Diagnostics;
+using System.Linq;
 
 namespace Microsoft.Z3
 {
     /// <summary>
     /// Lambda expressions.
     /// </summary>
-    [ContractVerification(true)]
     public class Lambda : ArrayExpr
     {
         /// <summary>
@@ -43,7 +43,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<Symbol[]>() != null);
 
                 uint n = NumBound;
                 Symbol[] res = new Symbol[n];
@@ -60,7 +59,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<Sort[]>() != null);
 
                 uint n = NumBound;
                 Sort[] res = new Sort[n];
@@ -77,7 +75,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<BoolExpr>() != null);
 
                 return new BoolExpr(Context, Native.Z3_get_quantifier_body(Context.nCtx, NativeObject));
             }
@@ -94,17 +91,16 @@ namespace Microsoft.Z3
         }
 
         #region Internal
-        [ContractVerification(false)] // F: Clousot ForAll decompilation gets confused below. Setting verification off until I fixed the bug
         internal Lambda(Context ctx, Sort[] sorts, Symbol[] names, Expr body)
             : base(ctx, IntPtr.Zero)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
-            Contract.Requires(sorts != null);
+            Debug.Assert(sorts != null);
-            Contract.Requires(names != null);
+            Debug.Assert(names != null);
-            Contract.Requires(body != null);
+            Debug.Assert(body != null);
-            Contract.Requires(sorts.Length == names.Length);
+            Debug.Assert(sorts.Length == names.Length);
-            Contract.Requires(Contract.ForAll(sorts, s => s != null));
+            Debug.Assert(sorts.All(s => s != null));
-            Contract.Requires(Contract.ForAll(names, n => n != null));
+            Debug.Assert(names.All(n => n != null));
             Context.CheckContextMatch<Sort>(sorts);
             Context.CheckContextMatch<Symbol>(names);
             Context.CheckContextMatch(body);
@@ -119,14 +115,13 @@ namespace Microsoft.Z3
             
         }
 
-        [ContractVerification(false)] // F: Clousot ForAll decompilation gets confused below. Setting verification off until I fixed the bug
         internal Lambda(Context ctx, Expr[] bound, Expr body)
             : base(ctx, IntPtr.Zero)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
-            Contract.Requires(body != null);
+            Debug.Assert(body != null);
 
-            Contract.Requires(bound != null && bound.Length > 0 && Contract.ForAll(bound, n => n != null));
+            Debug.Assert(bound != null && bound.Length > 0 && bound.All(n => n != null));
 
             Context.CheckContextMatch<Expr>(bound);
             Context.CheckContextMatch(body);
@@ -137,7 +132,7 @@ namespace Microsoft.Z3
         }
 
 
-        internal Lambda(Context ctx, IntPtr obj) : base(ctx, obj) { Contract.Requires(ctx != null); }
+        internal Lambda(Context ctx, IntPtr obj) : base(ctx, obj) { Debug.Assert(ctx != null); }
 
 #if DEBUG
         internal override void CheckNativeObject(IntPtr obj)

src/api/dotnet/ListSort.cs

@@ -17,15 +17,14 @@ Notes:
     
 --*/
 
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
     /// <summary>
     /// List sorts.
     /// </summary>
-    [ContractVerification(true)]
     public class ListSort : Sort
     {
         /// <summary>
@@ -35,7 +34,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<FuncDecl>() != null);
                 return new FuncDecl(Context, Native.Z3_get_datatype_sort_constructor(Context.nCtx, NativeObject, 0));                                
             }
         }
@@ -47,7 +45,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<Expr>() != null);
                 return Context.MkApp(NilDecl);
             }
         }
@@ -59,7 +56,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<FuncDecl>() != null);
                 return new FuncDecl(Context, Native.Z3_get_datatype_sort_recognizer(Context.nCtx, NativeObject, 0));
             }
         }
@@ -71,7 +67,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<FuncDecl>() != null);
                 return new FuncDecl(Context, Native.Z3_get_datatype_sort_constructor(Context.nCtx, NativeObject, 1));
             }
         }
@@ -84,7 +79,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<FuncDecl>() != null);
                 return new FuncDecl(Context, Native.Z3_get_datatype_sort_recognizer(Context.nCtx, NativeObject, 1));
             }
         }
@@ -96,7 +90,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<FuncDecl>() != null);
                 return new FuncDecl(Context, Native.Z3_get_datatype_sort_constructor_accessor(Context.nCtx, NativeObject, 1, 0));
             }
         }
@@ -108,7 +101,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<FuncDecl>() != null);
                 return new FuncDecl(Context, Native.Z3_get_datatype_sort_constructor_accessor(Context.nCtx, NativeObject, 1, 1));
             }
         }
@@ -117,9 +109,9 @@ namespace Microsoft.Z3
         internal ListSort(Context ctx, Symbol name, Sort elemSort)
             : base(ctx, IntPtr.Zero)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
-            Contract.Requires(name != null);
+            Debug.Assert(name != null);
-            Contract.Requires(elemSort != null);
+            Debug.Assert(elemSort != null);
 
             IntPtr inil = IntPtr.Zero, iisnil = IntPtr.Zero, 
                    icons = IntPtr.Zero, iiscons = IntPtr.Zero,

src/api/dotnet/Log.cs

@@ -17,8 +17,8 @@ Notes:
     
 --*/
 
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
@@ -29,7 +29,6 @@ namespace Microsoft.Z3
     /// Note that this is a global, static log and if multiple Context 
     /// objects are created, it logs the interaction with all of them.
     /// </remarks>
-    [ContractVerification(true)]
     public static class Log
     {
         private static bool m_is_open = false;
@@ -59,7 +58,7 @@ namespace Microsoft.Z3
         /// </summary>    
         public static void Append(string s)
         {
-            Contract.Requires(isOpen());
+            Debug.Assert(isOpen());
 
             if (!m_is_open)
                 throw new Z3Exception("Log cannot be closed.");
@@ -70,7 +69,6 @@ namespace Microsoft.Z3
         /// Checks whether the interaction log is opened.
         /// </summary>
         /// <returns>True if the interaction log is open, false otherwise.</returns>
-        [Pure]
         public static bool isOpen()
         {
             return m_is_open;

src/api/dotnet/Model.cs

@@ -18,7 +18,7 @@ Notes:
 --*/
 
 using System;
-using System.Diagnostics.Contracts;
+using System.Diagnostics;
 using System.Collections.Generic;
 
 namespace Microsoft.Z3
@@ -26,7 +26,6 @@ namespace Microsoft.Z3
     /// <summary>
     /// A Model contains interpretations (assignments) of constants and functions. 
     /// </summary>
-    [ContractVerification(true)]
     public class Model : Z3Object
     {
         /// <summary>
@@ -36,7 +35,7 @@ namespace Microsoft.Z3
         /// <returns>An expression if the constant has an interpretation in the model, null otherwise.</returns>
         public Expr ConstInterp(Expr a)
         {
-            Contract.Requires(a != null);
+            Debug.Assert(a != null);
 
             Context.CheckContextMatch(a);
             return ConstInterp(a.FuncDecl);
@@ -49,7 +48,7 @@ namespace Microsoft.Z3
         /// <returns>An expression if the function has an interpretation in the model, null otherwise.</returns>    
         public Expr ConstInterp(FuncDecl f)
         {
-            Contract.Requires(f != null);
+            Debug.Assert(f != null);
 
             Context.CheckContextMatch(f);
             if (f.Arity != 0 ||
@@ -70,7 +69,7 @@ namespace Microsoft.Z3
         /// <returns>A FunctionInterpretation if the function has an interpretation in the model, null otherwise.</returns> 
         public FuncInterp FuncInterp(FuncDecl f)
         {
-            Contract.Requires(f != null);
+            Debug.Assert(f != null);
 
             Context.CheckContextMatch(f);
 
@@ -122,7 +121,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<FuncDecl[]>() != null);
 
                 uint n = NumConsts;
                 FuncDecl[] res = new FuncDecl[n];
@@ -165,7 +163,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<FuncDecl[]>() != null);
 
                 uint n = NumFuncs;
                 FuncDecl[] res = new FuncDecl[n];
@@ -182,7 +179,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<FuncDecl[]>() != null);
 
                 uint nFuncs = NumFuncs;
                 uint nConsts = NumConsts;
@@ -223,8 +219,7 @@ namespace Microsoft.Z3
         /// <returns>The evaluation of <paramref name="t"/> in the model.</returns>        
         public Expr Eval(Expr t, bool completion = false)
         {
-            Contract.Requires(t != null);
+            Debug.Assert(t != null);
-            Contract.Ensures(Contract.Result<Expr>() != null);
 
             IntPtr v = IntPtr.Zero;
             if (Native.Z3_model_eval(Context.nCtx, NativeObject, t.NativeObject, (byte)(completion ? 1 : 0), ref v) == (byte)0)
@@ -238,8 +233,7 @@ namespace Microsoft.Z3
         /// </summary>        
         public Expr Evaluate(Expr t, bool completion = false)
         {
-            Contract.Requires(t != null);
+            Debug.Assert(t != null);
-            Contract.Ensures(Contract.Result<Expr>() != null);
 
             return Eval(t, completion);
         }
@@ -263,7 +257,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<Sort[]>() != null);
 
                 uint n = NumSorts;
                 Sort[] res = new Sort[n];
@@ -281,8 +274,7 @@ namespace Microsoft.Z3
         /// <returns>An array of expressions, where each is an element of the universe of <paramref name="s"/></returns>
         public Expr[] SortUniverse(Sort s)
         {
-            Contract.Requires(s != null);
+            Debug.Assert(s != null);
-            Contract.Ensures(Contract.Result<Expr[]>() != null);
 
             ASTVector av = new ASTVector(Context, Native.Z3_model_get_sort_universe(Context.nCtx, NativeObject, s.NativeObject));            
             return av.ToExprArray();
@@ -301,7 +293,7 @@ namespace Microsoft.Z3
         internal Model(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
 
         internal class DecRefQueue : IDecRefQueue

src/api/dotnet/Optimize.cs

@@ -19,14 +19,14 @@ Notes:
 
 using System;
 using System.Collections.Generic;
-using System.Diagnostics.Contracts;
+using System.Diagnostics;
+using System.Linq;
 
 namespace Microsoft.Z3
 {
     /// <summary>
     /// Object for managing optimizization context
     /// </summary>
-    [ContractVerification(true)]
     public class Optimize : Z3Object
     {
         /// <summary>
@@ -36,7 +36,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<string>() != null);
                 return Native.Z3_optimize_get_help(Context.nCtx, NativeObject);
             }
         }
@@ -48,7 +47,7 @@ namespace Microsoft.Z3
         {
             set
             {
-                Contract.Requires(value != null);
+                Debug.Assert(value != null);
                 Context.CheckContextMatch(value);
                 Native.Z3_optimize_set_params(Context.nCtx, NativeObject, value.NativeObject);
             }
@@ -99,8 +98,8 @@ namespace Microsoft.Z3
         /// </summary>   
         private void AddConstraints(IEnumerable<BoolExpr> constraints)
         {
-            Contract.Requires(constraints != null);
+            Debug.Assert(constraints != null);
-            Contract.Requires(Contract.ForAll(constraints, c => c != null));
+            Debug.Assert(constraints.All(c => c != null));
 
             Context.CheckContextMatch(constraints);
             foreach (BoolExpr a in constraints)
@@ -248,7 +247,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<Expr[]>() != null);
 
                 ASTVector core = new ASTVector(Context, Native.Z3_optimize_get_unsat_core(Context.nCtx, NativeObject));                
                 return core.ToBoolExprArray();
@@ -319,7 +317,6 @@ namespace Microsoft.Z3
         {
             get 
             {
-                Contract.Ensures(Contract.Result<string>() != null);
                 return Native.Z3_optimize_get_reason_unknown(Context.nCtx, NativeObject);
             }
         }
@@ -357,7 +354,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<BoolExpr[]>() != null);
 
                 ASTVector assertions = new ASTVector(Context, Native.Z3_optimize_get_assertions(Context.nCtx, NativeObject));
                 return assertions.ToBoolExprArray();
@@ -371,7 +367,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<Expr[]>() != null);
 
                 ASTVector objectives = new ASTVector(Context, Native.Z3_optimize_get_objectives(Context.nCtx, NativeObject));
                 return objectives.ToExprArray();
@@ -386,7 +381,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<Statistics>() != null);
 
                 return new Statistics(Context, Native.Z3_optimize_get_statistics(Context.nCtx, NativeObject));
             }
@@ -397,12 +391,12 @@ namespace Microsoft.Z3
         internal Optimize(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         internal Optimize(Context ctx)
             : base(ctx, Native.Z3_mk_optimize(ctx.nCtx))
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
 
         internal class DecRefQueue : IDecRefQueue

src/api/dotnet/ParamDescrs.cs

@@ -17,15 +17,14 @@ Notes:
     
 --*/
 
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
     /// <summary>
     /// A ParamDescrs describes a set of parameters.
     /// </summary>
-    [ContractVerification(true)]
     public class ParamDescrs : Z3Object
     {
         /// <summary>
@@ -33,7 +32,7 @@ namespace Microsoft.Z3
         /// </summary>
         public void Validate(Params p)
         {
-            Contract.Requires(p != null);
+            Debug.Assert(p != null);
             Native.Z3_params_validate(Context.nCtx, p.NativeObject, NativeObject);
         }
 
@@ -42,7 +41,7 @@ namespace Microsoft.Z3
         /// </summary>
         public Z3_param_kind GetKind(Symbol name)
         {
-            Contract.Requires(name != null);
+            Debug.Assert(name != null);
             return (Z3_param_kind)Native.Z3_param_descrs_get_kind(Context.nCtx, NativeObject, name.NativeObject);
         }
 
@@ -51,7 +50,7 @@ namespace Microsoft.Z3
         /// </summary>
         public string GetDocumentation(Symbol name)
         {
-            Contract.Requires(name != null);
+            Debug.Assert(name != null);
             return Native.Z3_param_descrs_get_documentation(Context.nCtx, NativeObject, name.NativeObject);
         }
 
@@ -91,7 +90,7 @@ namespace Microsoft.Z3
         internal ParamDescrs(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
 
         internal class DecRefQueue : IDecRefQueue

src/api/dotnet/Params.cs

@@ -17,15 +17,14 @@ Notes:
     
 --*/
 
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
     /// <summary>
     /// A Params objects represents a configuration in the form of Symbol/value pairs.
     /// </summary>
-    [ContractVerification(true)]
     public class Params : Z3Object
     {
         /// <summary>
@@ -33,7 +32,7 @@ namespace Microsoft.Z3
         /// </summary>
         public Params Add(Symbol name, bool value)
         {
-            Contract.Requires(name != null);
+            Debug.Assert(name != null);
 
             Native.Z3_params_set_bool(Context.nCtx, NativeObject, name.NativeObject, (byte)(value ? 1 : 0));
             return this;
@@ -44,7 +43,7 @@ namespace Microsoft.Z3
         /// </summary>
         public Params Add(Symbol name, uint value)
         {
-            Contract.Requires(name != null);
+            Debug.Assert(name != null);
 
             Native.Z3_params_set_uint(Context.nCtx, NativeObject, name.NativeObject, value);
             return this;
@@ -55,7 +54,7 @@ namespace Microsoft.Z3
         /// </summary>
         public Params Add(Symbol name, double value)
         {
-            Contract.Requires(name != null);            
+            Debug.Assert(name != null);            
 
             Native.Z3_params_set_double(Context.nCtx, NativeObject, name.NativeObject, value);
             return this;
@@ -66,7 +65,7 @@ namespace Microsoft.Z3
         /// </summary>
         public Params Add(Symbol name, string value)
         {
-            Contract.Requires(value != null);
+            Debug.Assert(value != null);
 
             Native.Z3_params_set_symbol(Context.nCtx, NativeObject, name.NativeObject, Context.MkSymbol(value).NativeObject);
             return this;
@@ -77,8 +76,8 @@ namespace Microsoft.Z3
         /// </summary>
         public Params Add(Symbol name, Symbol value)
         {
-            Contract.Requires(name != null);
+            Debug.Assert(name != null);
-            Contract.Requires(value != null);
+            Debug.Assert(value != null);
 
             Native.Z3_params_set_symbol(Context.nCtx, NativeObject, name.NativeObject, value.NativeObject);
             return this;
@@ -117,7 +116,7 @@ namespace Microsoft.Z3
         /// </summary>
         public Params Add(string name, Symbol value)
         {
-            Contract.Requires(value != null);
+            Debug.Assert(value != null);
 
             Native.Z3_params_set_symbol(Context.nCtx, NativeObject, Context.MkSymbol(name).NativeObject, value.NativeObject);
             return this;
@@ -128,8 +127,8 @@ namespace Microsoft.Z3
         /// </summary>
         public Params Add(string name, string value)
         {
-            Contract.Requires(name != null);
+            Debug.Assert(name != null);
-            Contract.Requires(value != null);
+            Debug.Assert(value != null);
 
             Native.Z3_params_set_symbol(Context.nCtx, NativeObject, Context.MkSymbol(name).NativeObject, Context.MkSymbol(value).NativeObject);
             return this;
@@ -147,7 +146,7 @@ namespace Microsoft.Z3
         internal Params(Context ctx)
             : base(ctx, Native.Z3_mk_params(ctx.nCtx))
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
 
         internal class DecRefQueue : IDecRefQueue

src/api/dotnet/Pattern.cs

@@ -17,9 +17,9 @@ Notes:
     
 --*/
 
+using System.Diagnostics;
 using System;
 using System.Runtime.InteropServices;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
@@ -28,7 +28,6 @@ namespace Microsoft.Z3
     /// non-empty.  If the list comprises of more than one term, it is
     /// also called a multi-pattern.
     /// </summary>
-    [ContractVerification(true)]
     public class Pattern : AST
     {
         /// <summary>
@@ -46,7 +45,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<Expr[]>() != null);
 
                 uint n = NumTerms;
                 Expr[] res = new Expr[n];
@@ -68,7 +66,7 @@ namespace Microsoft.Z3
         internal Pattern(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         #endregion
     }

src/api/dotnet/Probe.cs

@@ -17,9 +17,9 @@ Notes:
     
 --*/
 
+using System.Diagnostics;
 using System;
 using System.Runtime.InteropServices;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
@@ -30,7 +30,6 @@ namespace Microsoft.Z3
     /// and <c>Context.ProbeNames</c>.
     /// It may also be obtained using the command <c>(help-tactic)</c> in the SMT 2.0 front-end.
     /// </summary>
-    [ContractVerification(true)]
     public class Probe : Z3Object
     {
         /// <summary>
@@ -40,7 +39,7 @@ namespace Microsoft.Z3
         /// "Boolean" probes return 0.0 for false, and a value different from 0.0 for true.</returns>
         public double Apply(Goal g)
         {
-            Contract.Requires(g != null);
+            Debug.Assert(g != null);
 
             Context.CheckContextMatch(g);
             return Native.Z3_probe_apply(Context.nCtx, NativeObject, g.NativeObject);
@@ -53,7 +52,7 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Requires(g != null);
+                Debug.Assert(g != null);
 
                 return Apply(g);
             }
@@ -63,12 +62,12 @@ namespace Microsoft.Z3
         internal Probe(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         internal Probe(Context ctx, string name)
             : base(ctx, Native.Z3_mk_probe(ctx.nCtx, name))
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
 
         internal class DecRefQueue : IDecRefQueue

src/api/dotnet/Quantifier.cs

@@ -18,14 +18,14 @@ Notes:
 --*/
 
 using System;
-using System.Diagnostics.Contracts;
+using System.Diagnostics;
+using System.Linq;
 
 namespace Microsoft.Z3
 {
     /// <summary>
     /// Quantifier expressions.
     /// </summary>
-    [ContractVerification(true)]
     public class Quantifier : BoolExpr
     {
         /// <summary>
@@ -67,7 +67,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<Pattern[]>() != null);
 
                 uint n = NumPatterns;
                 Pattern[] res = new Pattern[n];
@@ -92,7 +91,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<Pattern[]>() != null);
 
                 uint n = NumNoPatterns;
                 Pattern[] res = new Pattern[n];
@@ -117,7 +115,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<Symbol[]>() != null);
 
                 uint n = NumBound;
                 Symbol[] res = new Symbol[n];
@@ -134,7 +131,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<Sort[]>() != null);
 
                 uint n = NumBound;
                 Sort[] res = new Sort[n];
@@ -151,7 +147,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<BoolExpr>() != null);
 
                 return new BoolExpr(Context, Native.Z3_get_quantifier_body(Context.nCtx, NativeObject));
             }
@@ -168,19 +163,18 @@ namespace Microsoft.Z3
         }
 
         #region Internal
-        [ContractVerification(false)] // F: Clousot ForAll decompilation gets confused below. Setting verification off until I fixed the bug
         internal Quantifier(Context ctx, bool isForall, Sort[] sorts, Symbol[] names, Expr body, uint weight = 1, Pattern[] patterns = null, Expr[] noPatterns = null, Symbol quantifierID = null, Symbol skolemID = null)
             : base(ctx, IntPtr.Zero)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
-            Contract.Requires(sorts != null);
+            Debug.Assert(sorts != null);
-            Contract.Requires(names != null);
+            Debug.Assert(names != null);
-            Contract.Requires(body != null);
+            Debug.Assert(body != null);
-            Contract.Requires(sorts.Length == names.Length);
+            Debug.Assert(sorts.Length == names.Length);
-            Contract.Requires(Contract.ForAll(sorts, s => s != null));
+            Debug.Assert(sorts.All(s => s != null));
-            Contract.Requires(Contract.ForAll(names, n => n != null));
+            Debug.Assert(names.All(n => n != null));
-            Contract.Requires(patterns == null || Contract.ForAll(patterns, p => p != null));
+            Debug.Assert(patterns == null || patterns.All(p => p != null));
-            Contract.Requires(noPatterns == null || Contract.ForAll(noPatterns, np => np != null));
+            Debug.Assert(noPatterns == null || noPatterns.All(np => np != null));
 
             Context.CheckContextMatch<Pattern>(patterns);
             Context.CheckContextMatch<Expr>(noPatterns);
@@ -211,16 +205,15 @@ namespace Microsoft.Z3
             }
         }
 
-        [ContractVerification(false)] // F: Clousot ForAll decompilation gets confused below. Setting verification off until I fixed the bug
         internal Quantifier(Context ctx, bool isForall, Expr[] bound, Expr body, uint weight = 1, Pattern[] patterns = null, Expr[] noPatterns = null, Symbol quantifierID = null, Symbol skolemID = null)
             : base(ctx, IntPtr.Zero)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
-            Contract.Requires(body != null);
+            Debug.Assert(body != null);
 
-            Contract.Requires(patterns == null || Contract.ForAll(patterns, p => p != null));
+            Debug.Assert(patterns == null || patterns.All(p => p != null));
-            Contract.Requires(noPatterns == null || Contract.ForAll(noPatterns, np => np != null));
+            Debug.Assert(noPatterns == null || noPatterns.All(np => np != null));
-            Contract.Requires(bound == null || Contract.ForAll(bound, n => n != null));
+            Debug.Assert(bound == null || bound.All(n => n != null));
 
             Context.CheckContextMatch<Expr>(noPatterns);
             Context.CheckContextMatch<Pattern>(patterns);
@@ -246,7 +239,7 @@ namespace Microsoft.Z3
         }
 
 
-        internal Quantifier(Context ctx, IntPtr obj) : base(ctx, obj) { Contract.Requires(ctx != null); }
+        internal Quantifier(Context ctx, IntPtr obj) : base(ctx, obj) { Debug.Assert(ctx != null); }
 
 #if DEBUG
         internal override void CheckNativeObject(IntPtr obj)

src/api/dotnet/RatNum.cs

@@ -16,8 +16,8 @@ Author:
 Notes:
     
 --*/
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
 
 #if !FRAMEWORK_LT_4
 using System.Numerics;
@@ -28,7 +28,6 @@ namespace Microsoft.Z3
     /// <summary>
     /// Rational Numerals
     /// </summary>
-    [ContractVerification(true)]
     public class RatNum : RealExpr
     {
         /// <summary>
@@ -38,7 +37,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<IntNum>() != null);
 
                 return new IntNum(Context, Native.Z3_get_numerator(Context.nCtx, NativeObject));
             }
@@ -51,7 +49,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<IntNum>() != null);
 
                 return new IntNum(Context, Native.Z3_get_denominator(Context.nCtx, NativeObject));
             }
@@ -112,7 +109,7 @@ namespace Microsoft.Z3
         internal RatNum(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         #endregion
     }

src/api/dotnet/ReExpr.cs

@@ -16,12 +16,12 @@ Author:
 Notes:
     
 --*/
+using System.Diagnostics;
 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
@@ -35,7 +35,7 @@ namespace Microsoft.Z3
         internal ReExpr(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         #endregion
     }

src/api/dotnet/ReSort.cs

@@ -17,8 +17,8 @@ Notes:
     
 --*/
 
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
@@ -31,12 +31,12 @@ namespace Microsoft.Z3
         internal ReSort(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         internal ReSort(Context ctx)
             : base(ctx, Native.Z3_mk_int_sort(ctx.nCtx))
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         #endregion
     }

src/api/dotnet/RealExpr.cs

@@ -16,12 +16,12 @@ Author:
 Notes:
     
 --*/
+using System.Diagnostics;
 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
@@ -35,7 +35,7 @@ namespace Microsoft.Z3
         internal RealExpr(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         #endregion
     }

src/api/dotnet/RealSort.cs

@@ -17,8 +17,8 @@ Notes:
     
 --*/
 
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
@@ -31,12 +31,12 @@ namespace Microsoft.Z3
         internal RealSort(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         internal RealSort(Context ctx)
             : base(ctx, Native.Z3_mk_real_sort(ctx.nCtx))
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         #endregion
     }

src/api/dotnet/RelationSort.cs

@@ -17,15 +17,14 @@ Notes:
     
 --*/
 
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
     /// <summary>
     /// Relation sorts.
     /// </summary>
-    [ContractVerification(true)]
     public class RelationSort : Sort
     {
         /// <summary>
@@ -43,7 +42,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<Sort[]>() != null);
 
                 if (m_columnSorts != null)
                     return m_columnSorts;
@@ -62,7 +60,7 @@ namespace Microsoft.Z3
         internal RelationSort(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         #endregion
     }

src/api/dotnet/SeqExpr.cs

@@ -16,12 +16,12 @@ Author:
 Notes:
     
 --*/
+using System.Diagnostics;
 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
@@ -35,7 +35,7 @@ namespace Microsoft.Z3
         internal SeqExpr(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         #endregion
     }

src/api/dotnet/SeqSort.cs

@@ -17,8 +17,8 @@ Notes:
     
 --*/
 
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
@@ -31,12 +31,12 @@ namespace Microsoft.Z3
         internal SeqSort(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         internal SeqSort(Context ctx)
             : base(ctx, Native.Z3_mk_int_sort(ctx.nCtx))
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         #endregion
     }

src/api/dotnet/SetSort.cs

@@ -17,28 +17,27 @@ Notes:
     
 --*/
 
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
     /// <summary>
     /// Set sorts.
     /// </summary>
-    [ContractVerification(true)]
     public class SetSort : Sort
     {
         #region Internal
         internal SetSort(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         internal SetSort(Context ctx, Sort ty)
             : base(ctx, Native.Z3_mk_set_sort(ctx.nCtx, ty.NativeObject))
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
-            Contract.Requires(ty != null);
+            Debug.Assert(ty != null);
         }
         #endregion
     }

src/api/dotnet/Solver.cs

@@ -18,16 +18,15 @@ Notes:
 --*/
 
 using System;
+using System.Diagnostics;
 using System.Linq;
 using System.Collections.Generic;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
     /// <summary>
     /// Solvers.
     /// </summary>
-    [ContractVerification(true)]
     public class Solver : Z3Object
     {
         /// <summary>
@@ -37,7 +36,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<string>() != null);
 
                 return Native.Z3_solver_get_help(Context.nCtx, NativeObject);
             }
@@ -50,7 +48,7 @@ namespace Microsoft.Z3
         {
             set
             {
-                Contract.Requires(value != null);
+                Debug.Assert(value != null);
 
                 Context.CheckContextMatch(value);
                 Native.Z3_solver_set_params(Context.nCtx, NativeObject, value.NativeObject);
@@ -152,8 +150,8 @@ namespace Microsoft.Z3
         /// </summary>        
         public void Assert(params BoolExpr[] constraints)
         {
-            Contract.Requires(constraints != null);
+            Debug.Assert(constraints != null);
-            Contract.Requires(Contract.ForAll(constraints, c => c != null));
+            Debug.Assert(constraints.All(c => c != null));
 
             Context.CheckContextMatch<BoolExpr>(constraints);
             foreach (BoolExpr a in constraints)
@@ -191,9 +189,9 @@ namespace Microsoft.Z3
         /// </remarks>        
         public void AssertAndTrack(BoolExpr[] constraints, BoolExpr[] ps)
         {
-            Contract.Requires(constraints != null);
+            Debug.Assert(constraints != null);
-            Contract.Requires(Contract.ForAll(constraints, c => c != null));
+            Debug.Assert(constraints.All(c => c != null));
-            Contract.Requires(Contract.ForAll(ps, c => c != null));
+            Debug.Assert(ps.All(c => c != null));
             Context.CheckContextMatch<BoolExpr>(constraints);
             Context.CheckContextMatch<BoolExpr>(ps);
             if (constraints.Length != ps.Length)
@@ -216,8 +214,8 @@ namespace Microsoft.Z3
         /// </remarks>        
         public void AssertAndTrack(BoolExpr constraint, BoolExpr p)
         {
-            Contract.Requires(constraint != null);
+            Debug.Assert(constraint != null);
-            Contract.Requires(p != null);
+            Debug.Assert(p != null);
             Context.CheckContextMatch(constraint);
             Context.CheckContextMatch(p);
                         
@@ -259,7 +257,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<BoolExpr[]>() != null);
 
                 ASTVector assertions = new ASTVector(Context, Native.Z3_solver_get_assertions(Context.nCtx, NativeObject));
                 return assertions.ToBoolExprArray();
@@ -273,7 +270,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<BoolExpr[]>() != null);
 
                 ASTVector assertions = new ASTVector(Context, Native.Z3_solver_get_units(Context.nCtx, NativeObject));
                 return assertions.ToBoolExprArray();
@@ -394,7 +390,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<Expr[]>() != null);
 
                 ASTVector core = new ASTVector(Context, Native.Z3_solver_get_unsat_core(Context.nCtx, NativeObject));                
                 return core.ToBoolExprArray();
@@ -408,7 +403,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<string>() != null);
 
                 return Native.Z3_solver_get_reason_unknown(Context.nCtx, NativeObject);
             }
@@ -455,8 +449,7 @@ namespace Microsoft.Z3
         /// </summary>
         public Solver Translate(Context ctx) 
         {
-             Contract.Requires(ctx != null);
+             Debug.Assert(ctx != null);
-             Contract.Ensures(Contract.Result<Solver>() != null);
              return new Solver(ctx, Native.Z3_solver_translate(Context.nCtx, NativeObject, ctx.nCtx));
         }
 
@@ -475,7 +468,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<Statistics>() != null);
 
                 return new Statistics(Context, Native.Z3_solver_get_statistics(Context.nCtx, NativeObject));
             }
@@ -493,7 +485,7 @@ namespace Microsoft.Z3
         internal Solver(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
             this.BacktrackLevel = uint.MaxValue;
         }
 

src/api/dotnet/Sort.cs

@@ -17,15 +17,14 @@ Notes:
 
 --*/
 
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
     /// <summary>
     /// The Sort class implements type information for ASTs.
     /// </summary>
-    [ContractVerification(true)]
     public class Sort : AST
     {
         /// <summary>
@@ -100,7 +99,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<Symbol>() != null);
                 return Symbol.Create(Context, Native.Z3_get_sort_name(Context.nCtx, NativeObject));
             }
         }
@@ -127,7 +125,7 @@ namespace Microsoft.Z3
         /// <summary>
         /// Sort constructor
         /// </summary>
-        internal Sort(Context ctx, IntPtr obj) : base(ctx, obj) { Contract.Requires(ctx != null); }
+        internal Sort(Context ctx, IntPtr obj) : base(ctx, obj) { Debug.Assert(ctx != null); }
 
 #if DEBUG
         internal override void CheckNativeObject(IntPtr obj)
@@ -138,11 +136,9 @@ namespace Microsoft.Z3
         }
 #endif
 
-        [ContractVerification(true)]
         new internal static Sort Create(Context ctx, IntPtr obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
-            Contract.Ensures(Contract.Result<Sort>() != null);
 
             switch ((Z3_sort_kind)Native.Z3_get_sort_kind(ctx.nCtx, obj))
             {

src/api/dotnet/Statistics.cs

@@ -18,14 +18,14 @@ Notes:
 --*/
 
 using System;
-using System.Diagnostics.Contracts;
+using System.Diagnostics;
+
 
 namespace Microsoft.Z3
 {
     /// <summary>
     /// Objects of this class track statistical information about solvers. 
     /// </summary>
-    [ContractVerification(true)]
     public class Statistics : Z3Object
     {
         /// <summary>
@@ -62,7 +62,6 @@ namespace Microsoft.Z3
             {
                 get
                 {
-                    Contract.Ensures(Contract.Result<string>() != null);
 
                     if (IsUInt)
                         return m_uint.ToString();
@@ -124,9 +123,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<Entry[]>() != null);
-                Contract.Ensures(Contract.Result<Entry[]>().Length == this.Size);
-                Contract.Ensures(Contract.ForAll(0, Contract.Result<Entry[]>().Length, j => Contract.Result<Entry[]>()[j] != null));
 
                 uint n = Size;
                 Entry[] res = new Entry[n];
@@ -153,7 +149,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<string[]>() != null);
 
                 uint n = Size;
                 string[] res = new string[n];
@@ -184,7 +179,7 @@ namespace Microsoft.Z3
         internal Statistics(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
 
         internal class DecRefQueue : IDecRefQueue

src/api/dotnet/Status.cs

@@ -17,6 +17,7 @@ Notes:
     
 --*/
 
+using System.Diagnostics;
 using System;
 
 namespace Microsoft.Z3

src/api/dotnet/StringSymbol.cs

@@ -18,8 +18,8 @@ Notes:
 --*/
 
 using System;
+using System.Diagnostics;
 using System.Runtime.InteropServices;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
@@ -27,7 +27,6 @@ namespace Microsoft.Z3
     /// <summary>
     /// Named symbols
     /// </summary>
-    [ContractVerification(true)]
     public class StringSymbol : Symbol
     {
         /// <summary>
@@ -38,7 +37,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<string>() != null);
 
                 if (!IsStringSymbol())
                     throw new Z3Exception("String requested from non-String symbol");
@@ -50,13 +48,13 @@ namespace Microsoft.Z3
         internal StringSymbol(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
 
         internal StringSymbol(Context ctx, string s)
             : base(ctx, Native.Z3_mk_string_symbol(ctx.nCtx, s))
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
 
 #if DEBUG

src/api/dotnet/Symbol.cs

@@ -18,15 +18,14 @@ Notes:
 --*/
 
 using System;
+using System.Diagnostics;
 using System.Runtime.InteropServices;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
     /// <summary>
     /// Symbols are used to name several term and type constructors.
     /// </summary>
-    [ContractVerification(true)]
     public class Symbol : Z3Object
     {
         /// <summary>
@@ -113,13 +112,12 @@ namespace Microsoft.Z3
         /// </summary>
         internal protected Symbol(Context ctx, IntPtr obj) : base(ctx, obj) 
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
 
         internal static Symbol Create(Context ctx, IntPtr obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
-            Contract.Ensures(Contract.Result<Symbol>() != null);
 
             switch ((Z3_symbol_kind)Native.Z3_get_symbol_kind(ctx.nCtx, obj))
             {

src/api/dotnet/Tactic.cs

@@ -18,7 +18,7 @@ Notes:
 --*/
 
 using System;
-using System.Diagnostics.Contracts;
+using System.Diagnostics;
 
 namespace Microsoft.Z3
 {
@@ -28,7 +28,6 @@ namespace Microsoft.Z3
     /// and <c>Context.TacticNames</c>.
     /// It may also be obtained using the command <c>(help-tactic)</c> in the SMT 2.0 front-end.
     /// </summary>
-    [ContractVerification(true)]
     public class Tactic : Z3Object
     {
         /// <summary>
@@ -38,7 +37,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<string>() != null);
 
                 return Native.Z3_tactic_get_help(Context.nCtx, NativeObject);
             }
@@ -59,8 +57,7 @@ namespace Microsoft.Z3
         /// </summary>
         public ApplyResult Apply(Goal g, Params p = null)
         {
-            Contract.Requires(g != null);
+            Debug.Assert(g != null);
-            Contract.Ensures(Contract.Result<ApplyResult>() != null);
 
             Context.CheckContextMatch(g);
             if (p == null)
@@ -79,8 +76,7 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Requires(g != null);
+                Debug.Assert(g != null);
-                Contract.Ensures(Contract.Result<ApplyResult>() != null);
 
                 return Apply(g);
             }
@@ -94,7 +90,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<Solver>() != null);
 
                 return Context.MkSolver(this);
             }
@@ -104,12 +99,12 @@ namespace Microsoft.Z3
         internal Tactic(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         internal Tactic(Context ctx, string name)
             : base(ctx, Native.Z3_mk_tactic(ctx.nCtx, name))
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
 
         /// <summary>

src/api/dotnet/TupleSort.cs

@@ -18,14 +18,13 @@ Notes:
 --*/
 
 using System;
-using System.Diagnostics.Contracts;
+using System.Diagnostics;
 
 namespace Microsoft.Z3
 {
     /// <summary>
     /// Tuple sorts.
     /// </summary>
-    [ContractVerification(true)]
     public class TupleSort : Sort
     {
         /// <summary>
@@ -35,7 +34,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<FuncDecl>() != null);
 
                 return new FuncDecl(Context, Native.Z3_get_tuple_sort_mk_decl(Context.nCtx, NativeObject));
             }
@@ -56,7 +54,6 @@ namespace Microsoft.Z3
         {
             get
             {
-                Contract.Ensures(Contract.Result<FuncDecl[]>() != null);
 
                 uint n = NumFields;
                 FuncDecl[] res = new FuncDecl[n];
@@ -70,8 +67,8 @@ namespace Microsoft.Z3
         internal TupleSort(Context ctx, Symbol name, uint numFields, Symbol[] fieldNames, Sort[] fieldSorts)
             : base(ctx, IntPtr.Zero)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
-            Contract.Requires(name != null);
+            Debug.Assert(name != null);
 
             IntPtr t = IntPtr.Zero;
             IntPtr[] f = new IntPtr[numFields];

src/api/dotnet/UninterpretedSort.cs

@@ -18,7 +18,7 @@ Notes:
 --*/
 
 using System;
-using System.Diagnostics.Contracts;
+using System.Diagnostics;
 
 namespace Microsoft.Z3
 {
@@ -31,13 +31,13 @@ namespace Microsoft.Z3
         internal UninterpretedSort(Context ctx, IntPtr obj)
             : base(ctx, obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
         }
         internal UninterpretedSort(Context ctx, Symbol s)
             : base(ctx, Native.Z3_mk_uninterpreted_sort(ctx.nCtx, s.NativeObject))
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
-            Contract.Requires(s != null);
+            Debug.Assert(s != null);
         }
         #endregion
     }

src/api/dotnet/Version.cs

@@ -17,8 +17,8 @@ Notes:
     
 --*/
 
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
 
 namespace Microsoft.Z3
 {
@@ -26,7 +26,6 @@ namespace Microsoft.Z3
     /// Version information.
     /// </summary>
     /// <remarks>Note that this class is static.</remarks>
-    [ContractVerification(true)]
     public static class Version
     {
         static Version() { }
@@ -99,7 +98,6 @@ namespace Microsoft.Z3
         /// </summary>
         new public static string ToString()
         {
-            Contract.Ensures(Contract.Result<string>() != null);
 
             uint major = 0, minor = 0, build = 0, revision = 0;
             Native.Z3_get_version(ref major, ref minor, ref build, ref revision);

src/api/dotnet/Z3Exception.cs

@@ -17,6 +17,7 @@ Notes:
 
 --*/
 
+using System.Diagnostics;
 using System;
 
 namespace Microsoft.Z3

src/api/dotnet/Z3Object.cs

@@ -17,8 +17,8 @@ Notes:
     
 --*/
 
+using System.Diagnostics;
 using System;
-using System.Diagnostics.Contracts;
 using System.Threading;
 using System.Collections.Generic;
 using System.Linq;
@@ -29,7 +29,6 @@ namespace Microsoft.Z3
     /// Internal base class for interfacing with native Z3 objects.
     /// Should not be used externally.
     /// </summary>
-    [ContractVerification(true)]
     public class Z3Object : IDisposable
     {
         /// <summary>
@@ -63,10 +62,9 @@ namespace Microsoft.Z3
 
         #region Object Invariant
         
-        [ContractInvariantMethod]
         private void ObjectInvariant()
         {
-            Contract.Invariant(this.m_ctx != null);
+            Debug.Assert(this.m_ctx != null);
         }
 
         #endregion
@@ -77,7 +75,7 @@ namespace Microsoft.Z3
 
         internal Z3Object(Context ctx)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
 
             Interlocked.Increment(ref ctx.refCount);
             m_ctx = ctx;
@@ -85,7 +83,7 @@ namespace Microsoft.Z3
 
         internal Z3Object(Context ctx, IntPtr obj)
         {
-            Contract.Requires(ctx != null);
+            Debug.Assert(ctx != null);
 
             Interlocked.Increment(ref ctx.refCount);
             m_ctx = ctx;
@@ -119,16 +117,12 @@ namespace Microsoft.Z3
         {
             get 
             {
-                Contract.Ensures(Contract.Result<Context>() != null);
                 return m_ctx; 
             }            
         }
 
-        [Pure]
         internal static IntPtr[] ArrayToNative(Z3Object[] a)
         {
-            Contract.Ensures(a == null || Contract.Result<IntPtr[]>() != null);
-            Contract.Ensures(a == null || Contract.Result<IntPtr[]>().Length == a.Length);
 
             if (a == null) return null;
             IntPtr[] an = new IntPtr[a.Length];
@@ -137,11 +131,8 @@ namespace Microsoft.Z3
             return an;
         }
 
-        [Pure]
         internal static IntPtr[] EnumToNative<T>(IEnumerable<T> a) where T : Z3Object
         {
-            Contract.Ensures(a == null || Contract.Result<IntPtr[]>() != null);
-            Contract.Ensures(a == null || Contract.Result<IntPtr[]>().Length == a.Count());
 
             if (a == null) return null;
             IntPtr[] an = new IntPtr[a.Count()];
@@ -154,7 +145,6 @@ namespace Microsoft.Z3
             return an;
         }
 
-        [Pure]
         internal static uint ArrayLength(Z3Object[] a)
         {
             return (a == null)?0:(uint)a.Length;