diff --git a/lib/symmetry_reduce_tactic.cpp b/lib/symmetry_reduce_tactic.cpp
index 5ca1dbcbf..0ee606da9 100644
--- a/lib/symmetry_reduce_tactic.cpp
+++ b/lib/symmetry_reduce_tactic.cpp
@@ -7,7 +7,7 @@ Module Name:
 
 Abstract:
 
-    Add symmetry breaking predicates to assertion sets.
+    Add symmetry breaking predicates to goals.
 
 Author:
 
@@ -20,7 +20,6 @@ Notes:
 
 --*/
 #include"tactical.h"
-#include"assertion_set.h"
 #include"for_each_expr.h"
 #include"map.h"
 #include"expr_replacer.h"
diff --git a/mk_make.py b/mk_make.py
index f66dcd75f..3500fac03 100644
--- a/mk_make.py
+++ b/mk_make.py
@@ -33,4 +33,10 @@ add_lib('simplifier', ['util', 'ast', 'rewriter', 'old_params'])
 # We must replace all occurrences of simplifier with rewriter.
 add_lib('model', ['util', 'ast', 'rewriter', 'simplifier', 'old_params'])
 add_lib('framework', ['util', 'ast', 'model', 'old_params', 'simplifier', 'rewriter'])
-
+# Assertion set is the old tactic framework used in Z3 3.x. It will be deleted as soon as we finish the porting old
+# code to the new tactic framework.
+add_lib('assertion_set', ['util', 'ast', 'framework', 'model', 'rewriter', 'old_params'])
+add_lib('normal_forms', ['util', 'ast', 'old_params', 'simplifier', 'rewriter', 'assertion_set', 'framework', 'model'])
+add_lib('smt', ['util', 'ast', 'assertion_set'])
+add_lib('pattern', ['util', 'ast'])
+add_lib('spc', ['util', 'ast', 'simplifier', 'pattern', 'model', 'old_params', 'normal_forms', 'rewriter'])
diff --git a/src/assertion_set/README b/src/assertion_set/README
new file mode 100644
index 000000000..ed699ed82
--- /dev/null
+++ b/src/assertion_set/README
@@ -0,0 +1 @@
+This module is obsolete. It is subsumed by the tactic module.
\ No newline at end of file
diff --git a/lib/assertion_set.cpp b/src/assertion_set/assertion_set.cpp
similarity index 100%
rename from lib/assertion_set.cpp
rename to src/assertion_set/assertion_set.cpp
diff --git a/lib/assertion_set.h b/src/assertion_set/assertion_set.h
similarity index 100%
rename from lib/assertion_set.h
rename to src/assertion_set/assertion_set.h
diff --git a/lib/assertion_set_rewriter.cpp b/src/assertion_set/assertion_set_rewriter.cpp
similarity index 100%
rename from lib/assertion_set_rewriter.cpp
rename to src/assertion_set/assertion_set_rewriter.cpp
diff --git a/lib/assertion_set_rewriter.h b/src/assertion_set/assertion_set_rewriter.h
similarity index 100%
rename from lib/assertion_set_rewriter.h
rename to src/assertion_set/assertion_set_rewriter.h
diff --git a/lib/assertion_set_strategy.cpp b/src/assertion_set/assertion_set_strategy.cpp
similarity index 87%
rename from lib/assertion_set_strategy.cpp
rename to src/assertion_set/assertion_set_strategy.cpp
index 3ba1fd9c9..209f20351 100644
--- a/lib/assertion_set_strategy.cpp
+++ b/src/assertion_set/assertion_set_strategy.cpp
@@ -21,7 +21,6 @@ Notes:
 #include"cooperate.h"
 #include"scoped_timer.h"
 #include"cancel_eh.h"
-#include"smt_solver.h"
 #include"front_end_params.h"
 #include"progress_callback.h"
 #include"params2front_end_params.h"
@@ -1201,164 +1200,6 @@ struct check_decided_test : public as_test {
 
 as_test * check_decided() { return alloc(check_decided_test); }
 
-class as_st_solver : public assertion_set_strategy {
-    scoped_ptr<front_end_params> m_params;
-    params_ref                   m_params_ref;
-    statistics                   m_stats;
-    std::string                  m_failure;
-    smt::solver *                m_ctx;
-    bool                         m_candidate_models;
-    symbol                       m_logic;
-    progress_callback *          m_callback;
-public:
-    as_st_solver(bool candidate_models):m_ctx(0), m_candidate_models(candidate_models), m_callback(0) {}
-    
-    front_end_params & fparams() {
-        if (!m_params)
-            m_params = alloc(front_end_params);
-        return *m_params;
-    }
-
-    struct scoped_init_ctx {
-        as_st_solver & m_owner;
-
-        scoped_init_ctx(as_st_solver & o, ast_manager & m):m_owner(o) {
-            smt::solver * new_ctx = alloc(smt::solver, m, o.fparams());
-            TRACE("as_solver", tout << "logic: " << o.m_logic << "\n";);
-            new_ctx->set_logic(o.m_logic);
-            if (o.m_callback) {
-                new_ctx->set_progress_callback(o.m_callback);
-            }
-            #pragma omp critical (as_st_solver) 
-            {
-                o.m_ctx = new_ctx;
-            }
-        }
-
-        ~scoped_init_ctx() {
-            smt::solver * d = m_owner.m_ctx;
-            #pragma omp critical (as_st_cancel)
-            {
-                m_owner.m_ctx = 0;
-            }
-            if (d)
-                dealloc(d);
-        }
-    };
-
-    virtual ~as_st_solver() {
-        SASSERT(m_ctx == 0);
-    }
-
-    virtual void updt_params(params_ref const & p) {
-        TRACE("as_solver", tout << "updt_params: " << p << "\n";);
-        m_params_ref = p;
-        params2front_end_params(m_params_ref, fparams());
-    }
-
-    virtual void collect_param_descrs(param_descrs & r) {
-    }
-
-    virtual void set_cancel(bool f) {
-        if (m_ctx)
-            m_ctx->set_cancel(f);
-    }
-
-    virtual void operator()(assertion_set & s, model_converter_ref & mc) {
-        SASSERT(is_well_sorted(s));
-        IF_VERBOSE(ST_VERBOSITY_LVL, verbose_stream() << "(smt-solver)" << std::endl;);
-        TRACE("as_solver", tout << "AUTO_CONFIG: " << fparams().m_auto_config << " HIDIV0: " << fparams().m_hi_div0 << " " 
-              << " PREPROCESS: " << fparams().m_preprocess << ", SOLVER:" << fparams().m_solver << "\n";);
-        TRACE("as_solver_detail", s.display(tout););        
-        ast_manager & m = s.m();
-        TRACE("as_solver_memory", tout << "wasted_size: " << m.get_allocator().get_wasted_size() << "\n";);        
-        // verbose_stream() << "wasted_size: " << m.get_allocator().get_wasted_size() << ", free_objs: " << m.get_allocator().get_num_free_objs() << "\n";
-        // m.get_allocator().consolidate();        
-        scoped_init_ctx  init(*this, m);
-        SASSERT(m_ctx != 0);
-        unsigned sz = s.size();
-        for (unsigned i = 0; i < sz; i++) {
-            expr * f = s.form(i);
-            m_ctx->assert_expr(f);
-        }
-        lbool r = m_ctx->setup_and_check();
-        m_ctx->collect_statistics(m_stats);
-        switch (r) {
-        case l_true: {
-            // the empty assertion set is trivially satifiable.
-            s.reset(); 
-            // store the model in a do nothin model converter.
-            model_ref md;
-            m_ctx->get_model(md);
-            mc = model2model_converter(md.get());
-            return;
-        }
-        case l_false:
-            // formula is unsat, reset the assertion set, and store false there.
-            s.reset();
-            s.assert_expr(m.mk_false(), m_ctx->get_proof());
-            return;
-        case l_undef:
-            if (m_candidate_models) {
-                switch (m_ctx->last_failure()) {
-                case smt::NUM_CONFLICTS:
-                case smt::THEORY:
-                case smt::QUANTIFIERS: {
-                    model_ref md;
-                    m_ctx->get_model(md);
-                    mc = model2model_converter(md.get());
-                    return;
-                }
-                default:
-                    break;
-                }
-            }
-            m_failure = m_ctx->last_failure_as_string();
-            throw strategy_exception(m_failure.c_str());
-        }
-    }
-
-    virtual void collect_statistics(statistics & st) const {
-        if (m_ctx)
-            m_ctx->collect_statistics(st); // ctx is still running...
-        else
-            st.copy(m_stats);
-    }
-
-    virtual void cleanup() {
-    }
-
-    virtual void reset_statistics() {
-        m_stats.reset();
-    }
-    
-    // for backward compatibility
-    virtual void set_front_end_params(front_end_params & p) {
-        m_params = alloc(front_end_params, p);
-        // must propagate the params_ref to fparams
-        params2front_end_params(m_params_ref, fparams());
-    }
-
-    virtual void set_logic(symbol const & l) {
-        m_logic = l;
-    }
-
-    virtual void set_progress_callback(progress_callback * callback) {
-        m_callback = callback;
-    }
-};
-
-as_st * mk_smt_solver_core(bool candidate_models) {
-    return alloc(as_st_solver, candidate_models);
-}
-
-as_st * mk_smt_solver(bool auto_config, bool candidate_models) {
-    as_st * solver = mk_smt_solver_core(candidate_models);
-    params_ref solver_p;    
-    solver_p.set_bool(":auto-config", auto_config);
-    return using_params(solver, solver_p);
-};
-
 /**
    \brief Execute strategy st on the given assertion set.
 */
diff --git a/lib/assertion_set_strategy.h b/src/assertion_set/assertion_set_strategy.h
similarity index 97%
rename from lib/assertion_set_strategy.h
rename to src/assertion_set/assertion_set_strategy.h
index c1209f6ae..0b02fad49 100644
--- a/lib/assertion_set_strategy.h
+++ b/src/assertion_set/assertion_set_strategy.h
@@ -167,9 +167,6 @@ as_test * check_as_size(unsigned l);
 as_test * check_decided();
 as_st * cond(as_test * c, as_st * t, as_st * e);
 
-as_st * mk_smt_solver_core(bool candidate_models = false);
-as_st * mk_smt_solver(bool auto_config = true, bool candidate_models = false);
-
 void exec(as_st * st, assertion_set & s, model_converter_ref & mc);
 lbool check_sat(as_st * st, assertion_set & s, model_ref & md, proof_ref & pr, std::string & reason_unknown);
 
@@ -207,8 +204,6 @@ public:
 
 #define MK_SIMPLE_ST_FACTORY(NAME, ST)  MK_ST_FACTORY(NAME, return ST;)
 
-MK_SIMPLE_ST_FACTORY(smt_solver_stf, mk_smt_solver());
-
 struct is_qfbv_test : public as_test {
     virtual bool operator()(assertion_set const & s) const {  return is_qfbv(s); }
 };
diff --git a/lib/assertion_set_util.cpp b/src/assertion_set/assertion_set_util.cpp
similarity index 100%
rename from lib/assertion_set_util.cpp
rename to src/assertion_set/assertion_set_util.cpp
diff --git a/lib/assertion_set_util.h b/src/assertion_set/assertion_set_util.h
similarity index 100%
rename from lib/assertion_set_util.h
rename to src/assertion_set/assertion_set_util.h
diff --git a/src/assertion_set/der_strategy.cpp b/src/assertion_set/der_strategy.cpp
new file mode 100644
index 000000000..ba294f2ee
--- /dev/null
+++ b/src/assertion_set/der_strategy.cpp
@@ -0,0 +1,94 @@
+/*++
+Copyright (c) 2012 Microsoft Corporation
+
+Module Name:
+
+    der_strategy.cpp
+
+Abstract:
+
+    DER strategy
+
+Author:
+
+    Leonardo de Moura (leonardo) 2012-10-20
+
+--*/
+#include"der_strategy.h"
+
+struct der_strategy::imp {
+    ast_manager &   m_manager;
+    der_rewriter    m_r;
+
+    imp(ast_manager & m):
+        m_manager(m),
+        m_r(m) {
+    }
+
+    ast_manager & m() const { return m_manager; }
+
+    void set_cancel(bool f) {
+        m_r.set_cancel(f);
+    }
+
+    void reset() {
+        m_r.reset();
+    }
+
+    void operator()(assertion_set & s) {
+        SASSERT(is_well_sorted(s));
+        as_st_report report("der", s);
+        TRACE("before_der", s.display(tout););
+        if (s.inconsistent())
+            return;
+        expr_ref   new_curr(m());
+        proof_ref  new_pr(m());
+        unsigned size = s.size();
+        for (unsigned idx = 0; idx < size; idx++) {
+            if (s.inconsistent())
+                break;
+            expr * curr = s.form(idx);
+            m_r(curr, new_curr, new_pr);
+            if (m().proofs_enabled()) {
+                proof * pr = s.pr(idx);
+                new_pr     = m().mk_modus_ponens(pr, new_pr);
+            }
+            s.update(idx, new_curr, new_pr);
+        }
+        s.elim_redundancies();
+        TRACE("after_der", s.display(tout););
+        SASSERT(is_well_sorted(s));
+    }
+};
+
+der_strategy::der_strategy(ast_manager & m) {
+    m_imp = alloc(imp, m);
+}
+
+der_strategy::~der_strategy() {
+    dealloc(m_imp);
+}
+
+void der_strategy::operator()(assertion_set & s) {
+    m_imp->operator()(s);
+}
+
+void der_strategy::set_cancel(bool f) {
+    if (m_imp)
+        m_imp->set_cancel(f);
+}
+
+void der_strategy::cleanup() {
+    ast_manager & m = m_imp->m();
+    imp * d = m_imp;
+    #pragma omp critical (as_st_cancel)
+    {
+        m_imp = 0;
+    }
+    dealloc(d);
+    d = alloc(imp, m);
+    #pragma omp critical (as_st_cancel)
+    {
+        m_imp = d;
+    }
+}
diff --git a/src/assertion_set/der_strategy.h b/src/assertion_set/der_strategy.h
new file mode 100644
index 000000000..ace90eb3c
--- /dev/null
+++ b/src/assertion_set/der_strategy.h
@@ -0,0 +1,47 @@
+/*++
+Copyright (c) 2012 Microsoft Corporation
+
+Module Name:
+
+    der_strategy.h
+
+Abstract:
+
+    DER strategy
+
+Author:
+
+    Leonardo de Moura (leonardo) 2012-10-20
+
+--*/
+#ifndef _DER_STRATEGY_H_
+#define _DER_STRATEGY_H_
+
+#include"der.h"
+#include"assertion_set_strategy.h"
+
+// TODO: delete obsolete class
+class der_strategy : public assertion_set_strategy {
+    struct     imp;
+    imp *      m_imp;
+public:
+    der_strategy(ast_manager & m);
+    virtual ~der_strategy();
+
+    void operator()(assertion_set & s);
+    
+    virtual void operator()(assertion_set & s, model_converter_ref & mc) {
+        operator()(s);
+        mc = 0;
+    }
+
+    virtual void cleanup();
+    virtual void set_cancel(bool f);
+};
+
+inline as_st * mk_der(ast_manager & m) {
+    return alloc(der_strategy, m);
+}
+
+
+#endif
diff --git a/lib/elim_var_model_converter.cpp b/src/assertion_set/elim_var_model_converter.cpp
similarity index 100%
rename from lib/elim_var_model_converter.cpp
rename to src/assertion_set/elim_var_model_converter.cpp
diff --git a/lib/elim_var_model_converter.h b/src/assertion_set/elim_var_model_converter.h
similarity index 100%
rename from lib/elim_var_model_converter.h
rename to src/assertion_set/elim_var_model_converter.h
diff --git a/lib/gaussian_elim.cpp b/src/assertion_set/gaussian_elim.cpp
similarity index 100%
rename from lib/gaussian_elim.cpp
rename to src/assertion_set/gaussian_elim.cpp
diff --git a/lib/gaussian_elim.h b/src/assertion_set/gaussian_elim.h
similarity index 100%
rename from lib/gaussian_elim.h
rename to src/assertion_set/gaussian_elim.h
diff --git a/src/assertion_set/num_occurs_assertion_set.cpp b/src/assertion_set/num_occurs_assertion_set.cpp
new file mode 100644
index 000000000..2f35d4b5c
--- /dev/null
+++ b/src/assertion_set/num_occurs_assertion_set.cpp
@@ -0,0 +1,29 @@
+/*++
+Copyright (c) 2012 Microsoft Corporation
+
+Module Name:
+
+    num_occurs_assertion_set.cpp
+
+Abstract:
+
+    TODO: delete
+
+Author:
+
+    Leonardo de Moura (leonardo) 2012-10-20.
+
+Revision History:
+
+--*/
+#include"num_occurs_assertion_set.h"
+#include"assertion_set.h"
+
+// TODO delete
+void num_occurs_as::operator()(assertion_set const & s) {
+    expr_fast_mark1   visited;
+    unsigned sz = s.size();
+    for (unsigned i = 0; i < sz; i++) {
+        process(s.form(i), visited);
+    }
+}
diff --git a/src/assertion_set/num_occurs_assertion_set.h b/src/assertion_set/num_occurs_assertion_set.h
new file mode 100644
index 000000000..50e8ac4e8
--- /dev/null
+++ b/src/assertion_set/num_occurs_assertion_set.h
@@ -0,0 +1,38 @@
+/*++
+Copyright (c) 2012 Microsoft Corporation
+
+Module Name:
+
+    num_occurs_assertion_set.h
+
+Abstract:
+
+    TODO: delete
+
+Author:
+
+    Leonardo de Moura (leonardo) 2012-10-20.
+
+Revision History:
+
+--*/
+#ifndef _NUM_OCCURS_AS_H_
+#define _NUM_OCCURS_AS_H_
+
+#include"num_occurs.h"
+
+class assertion_set;
+
+/**
+   \brief Functor for computing the number of occurrences of each sub-expression in a expression F.
+*/
+class num_occurs_as : public num_occurs { 
+public:
+    num_occurs_as(bool ignore_ref_count1 = false, bool ignore_quantifiers = false):
+        num_occurs(ignore_ref_count1, ignore_quantifiers) {
+    }
+
+    void operator()(assertion_set const & s); // TODO delete
+};
+
+#endif
diff --git a/lib/strategy_exception.cpp b/src/assertion_set/strategy_exception.cpp
similarity index 100%
rename from lib/strategy_exception.cpp
rename to src/assertion_set/strategy_exception.cpp
diff --git a/lib/strategy_exception.h b/src/assertion_set/strategy_exception.h
similarity index 100%
rename from lib/strategy_exception.h
rename to src/assertion_set/strategy_exception.h
diff --git a/lib/num_occurs.cpp b/src/ast/num_occurs.cpp
similarity index 82%
rename from lib/num_occurs.cpp
rename to src/ast/num_occurs.cpp
index ee4b76258..c5d50475e 100644
--- a/lib/num_occurs.cpp
+++ b/src/ast/num_occurs.cpp
@@ -18,8 +18,6 @@ Revision History:
 --*/
 
 #include"num_occurs.h"
-#include"assertion_set.h"
-#include"goal.h"
 
 void num_occurs::process(expr * t, expr_fast_mark1 & visited) {
     ptr_buffer<expr, 128> stack;
@@ -74,19 +72,3 @@ void num_occurs::operator()(unsigned num, expr * const * ts) {
     }
 }
 
-// TODO delete
-void num_occurs::operator()(assertion_set const & s) {
-    expr_fast_mark1   visited;
-    unsigned sz = s.size();
-    for (unsigned i = 0; i < sz; i++) {
-        process(s.form(i), visited);
-    }
-}
-
-void num_occurs::operator()(goal const & g) {
-    expr_fast_mark1   visited;
-    unsigned sz = g.size();
-    for (unsigned i = 0; i < sz; i++) {
-        process(g.form(i), visited);
-    }
-}
diff --git a/lib/num_occurs.h b/src/ast/num_occurs.h
similarity index 88%
rename from lib/num_occurs.h
rename to src/ast/num_occurs.h
index 01d160ac5..ecd77e356 100644
--- a/lib/num_occurs.h
+++ b/src/ast/num_occurs.h
@@ -22,13 +22,11 @@ Revision History:
 #include"ast.h"
 #include"obj_hashtable.h"
 
-class assertion_set; // TODO delete
-class goal;
-
 /**
    \brief Functor for computing the number of occurrences of each sub-expression in a expression F.
 */
 class num_occurs { 
+protected:
     bool m_ignore_ref_count1;
     bool m_ignore_quantifiers;
     obj_map<expr, unsigned>        m_num_occurs;
@@ -44,8 +42,6 @@ public:
     
     void operator()(expr * t);
     void operator()(unsigned num, expr * const * ts);
-    void operator()(assertion_set const & s); // TODO delete
-    void operator()(goal const & s);
 
     unsigned get_num_occs(expr * n) const { 
         unsigned val;
diff --git a/lib/occurs.cpp b/src/ast/occurs.cpp
similarity index 100%
rename from lib/occurs.cpp
rename to src/ast/occurs.cpp
diff --git a/lib/occurs.h b/src/ast/occurs.h
similarity index 100%
rename from lib/occurs.h
rename to src/ast/occurs.h
diff --git a/src/framework/der_tactic.cpp b/src/framework/der_tactic.cpp
new file mode 100644
index 000000000..c2245b409
--- /dev/null
+++ b/src/framework/der_tactic.cpp
@@ -0,0 +1,114 @@
+/*++
+Copyright (c) 2012 Microsoft Corporation
+
+Module Name:
+
+    der_tactic.cpp
+
+Abstract:
+
+    DER tactic
+
+Author:
+
+    Leonardo de Moura (leonardo) 2012-10-20
+
+--*/
+#include"der.h"
+#include"tactical.h"
+
+class der_tactic : public tactic {
+    struct imp {
+        ast_manager &   m_manager;
+        der_rewriter    m_r;
+        
+        imp(ast_manager & m):
+            m_manager(m),
+            m_r(m) {
+        }
+        
+        ast_manager & m() const { return m_manager; }
+        
+        void set_cancel(bool f) {
+            m_r.set_cancel(f);
+        }
+        
+        void reset() {
+            m_r.reset();
+        }
+        
+        void operator()(goal & g) {
+            SASSERT(g.is_well_sorted());
+            bool proofs_enabled = g.proofs_enabled();
+            tactic_report report("der", g);
+            TRACE("before_der", g.display(tout););
+            expr_ref   new_curr(m());
+            proof_ref  new_pr(m());
+            unsigned size = g.size();
+            for (unsigned idx = 0; idx < size; idx++) {
+                if (g.inconsistent())
+                    break;
+                expr * curr = g.form(idx);
+                m_r(curr, new_curr, new_pr);
+                if (proofs_enabled) {
+                    proof * pr = g.pr(idx);
+                    new_pr     = m().mk_modus_ponens(pr, new_pr);
+                }
+                g.update(idx, new_curr, new_pr, g.dep(idx));
+            }
+            g.elim_redundancies();
+            TRACE("after_der", g.display(tout););
+            SASSERT(g.is_well_sorted());
+        }
+    };
+
+    imp *      m_imp;
+
+public:
+    der_tactic(ast_manager & m) {
+        m_imp = alloc(imp, m);
+    }
+
+    virtual tactic * translate(ast_manager & m) {
+        return alloc(der_tactic, m);
+    }
+
+    virtual ~der_tactic() {
+        dealloc(m_imp);
+    }
+    
+    virtual void operator()(goal_ref const & in, 
+                            goal_ref_buffer & result, 
+                            model_converter_ref & mc, 
+                            proof_converter_ref & pc,
+                            expr_dependency_ref & core) {
+        mc = 0; pc = 0; core = 0;
+        (*m_imp)(*(in.get()));
+        in->inc_depth();
+        result.push_back(in.get());
+    }
+
+    virtual void cleanup() {
+        ast_manager & m = m_imp->m();
+        imp * d = m_imp;
+        #pragma omp critical (tactic_cancel)
+        {
+            m_imp = 0;
+        }
+        dealloc(d);
+        d = alloc(imp, m);
+        #pragma omp critical (tactic_cancel)
+        {
+            m_imp = d;
+        }
+    }
+    
+    virtual void set_cancel(bool f) {
+        if (m_imp)
+            m_imp->set_cancel(f);
+    }
+};
+
+tactic * mk_der_tactic(ast_manager & m) {
+    return alloc(der_tactic, m);
+}
diff --git a/src/framework/der_tactic.h b/src/framework/der_tactic.h
new file mode 100644
index 000000000..8e7d1453f
--- /dev/null
+++ b/src/framework/der_tactic.h
@@ -0,0 +1,25 @@
+/*++
+Copyright (c) 2012 Microsoft Corporation
+
+Module Name:
+
+    der_tactic.h
+
+Abstract:
+
+    DER tactic
+
+Author:
+
+    Leonardo de Moura (leonardo) 2012-10-20
+
+--*/
+#ifndef _DER_TACTIC_H_
+#define _DER_TACTIC_H_
+
+class ast_manager;
+class tactic;
+
+tactic * mk_der_tactic(ast_manager & m);
+
+#endif /* _DER_TACTIC_H_ */
diff --git a/src/framework/num_occurs_goal.cpp b/src/framework/num_occurs_goal.cpp
new file mode 100644
index 000000000..adc412434
--- /dev/null
+++ b/src/framework/num_occurs_goal.cpp
@@ -0,0 +1,27 @@
+/*++
+Copyright (c) 2012 Microsoft Corporation
+
+Module Name:
+
+    num_occurs_goal.cpp
+
+Abstract:
+
+
+Author:
+
+    Leonardo de Moura (leonardo) 2012-10-20.
+
+Revision History:
+
+--*/
+#include"num_occurs_goal.h"
+#include"goal.h"
+
+void num_occurs_goal::operator()(goal const & g) {
+    expr_fast_mark1   visited;
+    unsigned sz = g.size();
+    for (unsigned i = 0; i < sz; i++) {
+        process(g.form(i), visited);
+    }
+}
diff --git a/src/framework/num_occurs_goal.h b/src/framework/num_occurs_goal.h
new file mode 100644
index 000000000..5e6e0cc94
--- /dev/null
+++ b/src/framework/num_occurs_goal.h
@@ -0,0 +1,35 @@
+/*++
+Copyright (c) 2012 Microsoft Corporation
+
+Module Name:
+
+    num_occurs_goal.h
+
+Abstract:
+
+
+Author:
+
+    Leonardo de Moura (leonardo) 2012-10-20.
+
+Revision History:
+
+--*/
+#ifndef _NUM_OCCURS_GOAL_H_
+#define _NUM_OCCURS_GOAL_H_
+
+#include"num_occurs.h"
+
+class goal;
+
+class num_occurs_goal : public num_occurs { 
+public:
+    num_occurs_goal(bool ignore_ref_count1 = false, bool ignore_quantifiers = false):
+        num_occurs(ignore_ref_count1, ignore_quantifiers) {
+    }
+
+    void operator()(goal const & s);
+};
+
+
+#endif
diff --git a/lib/cnf.cpp b/src/normal_forms/cnf.cpp
similarity index 100%
rename from lib/cnf.cpp
rename to src/normal_forms/cnf.cpp
diff --git a/lib/cnf.h b/src/normal_forms/cnf.h
similarity index 100%
rename from lib/cnf.h
rename to src/normal_forms/cnf.h
diff --git a/lib/defined_names.cpp b/src/normal_forms/defined_names.cpp
similarity index 100%
rename from lib/defined_names.cpp
rename to src/normal_forms/defined_names.cpp
diff --git a/lib/defined_names.h b/src/normal_forms/defined_names.h
similarity index 100%
rename from lib/defined_names.h
rename to src/normal_forms/defined_names.h
diff --git a/lib/name_exprs.cpp b/src/normal_forms/name_exprs.cpp
similarity index 100%
rename from lib/name_exprs.cpp
rename to src/normal_forms/name_exprs.cpp
diff --git a/lib/name_exprs.h b/src/normal_forms/name_exprs.h
similarity index 100%
rename from lib/name_exprs.h
rename to src/normal_forms/name_exprs.h
diff --git a/lib/nnf.cpp b/src/normal_forms/nnf.cpp
similarity index 100%
rename from lib/nnf.cpp
rename to src/normal_forms/nnf.cpp
diff --git a/lib/nnf.h b/src/normal_forms/nnf.h
similarity index 100%
rename from lib/nnf.h
rename to src/normal_forms/nnf.h
diff --git a/lib/pull_quant.cpp b/src/normal_forms/pull_quant.cpp
similarity index 100%
rename from lib/pull_quant.cpp
rename to src/normal_forms/pull_quant.cpp
diff --git a/lib/pull_quant.h b/src/normal_forms/pull_quant.h
similarity index 100%
rename from lib/pull_quant.h
rename to src/normal_forms/pull_quant.h
diff --git a/lib/database.h b/src/pattern/database.h
similarity index 100%
rename from lib/database.h
rename to src/pattern/database.h
diff --git a/lib/database.smt b/src/pattern/database.smt
similarity index 100%
rename from lib/database.smt
rename to src/pattern/database.smt
diff --git a/lib/expr_pattern_match.cpp b/src/pattern/expr_pattern_match.cpp
similarity index 100%
rename from lib/expr_pattern_match.cpp
rename to src/pattern/expr_pattern_match.cpp
diff --git a/lib/expr_pattern_match.h b/src/pattern/expr_pattern_match.h
similarity index 100%
rename from lib/expr_pattern_match.h
rename to src/pattern/expr_pattern_match.h
diff --git a/lib/pattern_inference.cpp b/src/pattern/pattern_inference.cpp
similarity index 100%
rename from lib/pattern_inference.cpp
rename to src/pattern/pattern_inference.cpp
diff --git a/lib/pattern_inference.h b/src/pattern/pattern_inference.h
similarity index 100%
rename from lib/pattern_inference.h
rename to src/pattern/pattern_inference.h
diff --git a/lib/pattern_validation.cpp b/src/pattern/pattern_validation.cpp
similarity index 100%
rename from lib/pattern_validation.cpp
rename to src/pattern/pattern_validation.cpp
diff --git a/lib/pattern_validation.h b/src/pattern/pattern_validation.h
similarity index 100%
rename from lib/pattern_validation.h
rename to src/pattern/pattern_validation.h
diff --git a/lib/der.cpp b/src/rewriter/der.cpp
similarity index 77%
rename from lib/der.cpp
rename to src/rewriter/der.cpp
index 6df1a0105..4a4f438a7 100644
--- a/lib/der.cpp
+++ b/src/rewriter/der.cpp
@@ -25,7 +25,6 @@ Revision History:
 #include"ast_pp.h"
 #include"ast_ll_pp.h"
 #include"ast_smt2_pp.h"
-#include"tactical.h"
 
 static bool is_var(expr * e, unsigned num_decls) {
     return is_var(e) && to_var(e)->get_idx() < num_decls;
@@ -465,175 +464,4 @@ void der_rewriter::reset() {
     m_imp->reset();
 }
 
-struct der_strategy::imp {
-    ast_manager &   m_manager;
-    der_rewriter    m_r;
 
-    imp(ast_manager & m):
-        m_manager(m),
-        m_r(m) {
-    }
-
-    ast_manager & m() const { return m_manager; }
-
-    void set_cancel(bool f) {
-        m_r.set_cancel(f);
-    }
-
-    void reset() {
-        m_r.reset();
-    }
-
-    void operator()(assertion_set & s) {
-        SASSERT(is_well_sorted(s));
-        as_st_report report("der", s);
-        TRACE("before_der", s.display(tout););
-        if (s.inconsistent())
-            return;
-        expr_ref   new_curr(m());
-        proof_ref  new_pr(m());
-        unsigned size = s.size();
-        for (unsigned idx = 0; idx < size; idx++) {
-            if (s.inconsistent())
-                break;
-            expr * curr = s.form(idx);
-            m_r(curr, new_curr, new_pr);
-            if (m().proofs_enabled()) {
-                proof * pr = s.pr(idx);
-                new_pr     = m().mk_modus_ponens(pr, new_pr);
-            }
-            s.update(idx, new_curr, new_pr);
-        }
-        s.elim_redundancies();
-        TRACE("after_der", s.display(tout););
-        SASSERT(is_well_sorted(s));
-    }
-};
-
-der_strategy::der_strategy(ast_manager & m) {
-    m_imp = alloc(imp, m);
-}
-
-der_strategy::~der_strategy() {
-    dealloc(m_imp);
-}
-
-void der_strategy::operator()(assertion_set & s) {
-    m_imp->operator()(s);
-}
-
-void der_strategy::set_cancel(bool f) {
-    if (m_imp)
-        m_imp->set_cancel(f);
-}
-
-void der_strategy::cleanup() {
-    ast_manager & m = m_imp->m();
-    imp * d = m_imp;
-    #pragma omp critical (as_st_cancel)
-    {
-        m_imp = 0;
-    }
-    dealloc(d);
-    d = alloc(imp, m);
-    #pragma omp critical (as_st_cancel)
-    {
-        m_imp = d;
-    }
-}
-
-class der_tactic : public tactic {
-    struct imp {
-        ast_manager &   m_manager;
-        der_rewriter    m_r;
-        
-        imp(ast_manager & m):
-            m_manager(m),
-            m_r(m) {
-        }
-        
-        ast_manager & m() const { return m_manager; }
-        
-        void set_cancel(bool f) {
-            m_r.set_cancel(f);
-        }
-        
-        void reset() {
-            m_r.reset();
-        }
-        
-        void operator()(goal & g) {
-            SASSERT(g.is_well_sorted());
-            bool proofs_enabled = g.proofs_enabled();
-            tactic_report report("der", g);
-            TRACE("before_der", g.display(tout););
-            expr_ref   new_curr(m());
-            proof_ref  new_pr(m());
-            unsigned size = g.size();
-            for (unsigned idx = 0; idx < size; idx++) {
-                if (g.inconsistent())
-                    break;
-                expr * curr = g.form(idx);
-                m_r(curr, new_curr, new_pr);
-                if (proofs_enabled) {
-                    proof * pr = g.pr(idx);
-                    new_pr     = m().mk_modus_ponens(pr, new_pr);
-                }
-                g.update(idx, new_curr, new_pr, g.dep(idx));
-            }
-            g.elim_redundancies();
-            TRACE("after_der", g.display(tout););
-            SASSERT(g.is_well_sorted());
-        }
-    };
-
-    imp *      m_imp;
-
-public:
-    der_tactic(ast_manager & m) {
-        m_imp = alloc(imp, m);
-    }
-
-    virtual tactic * translate(ast_manager & m) {
-        return alloc(der_tactic, m);
-    }
-
-    virtual ~der_tactic() {
-        dealloc(m_imp);
-    }
-    
-    virtual void operator()(goal_ref const & in, 
-                            goal_ref_buffer & result, 
-                            model_converter_ref & mc, 
-                            proof_converter_ref & pc,
-                            expr_dependency_ref & core) {
-        mc = 0; pc = 0; core = 0;
-        (*m_imp)(*(in.get()));
-        in->inc_depth();
-        result.push_back(in.get());
-    }
-
-    virtual void cleanup() {
-        ast_manager & m = m_imp->m();
-        imp * d = m_imp;
-        #pragma omp critical (tactic_cancel)
-        {
-            m_imp = 0;
-        }
-        dealloc(d);
-        d = alloc(imp, m);
-        #pragma omp critical (tactic_cancel)
-        {
-            m_imp = d;
-        }
-    }
-    
-    virtual void set_cancel(bool f) {
-        if (m_imp)
-            m_imp->set_cancel(f);
-    }
-};
-
-tactic * mk_der_tactic(ast_manager & m) {
-    return alloc(der_tactic, m);
-}
diff --git a/lib/der.h b/src/rewriter/der.h
similarity index 91%
rename from lib/der.h
rename to src/rewriter/der.h
index 69f294fd4..a0be33c5c 100644
--- a/lib/der.h
+++ b/src/rewriter/der.h
@@ -23,7 +23,6 @@ Revision History:
 
 #include"ast.h"
 #include"var_subst.h"
-#include"assertion_set_strategy.h"
 
 /*
   New DER: the class DER (above) eliminates variables one by one.
@@ -184,32 +183,5 @@ public:
 
 typedef der_rewriter der_star; 
 
-// TODO: delete obsolete class
-class der_strategy : public assertion_set_strategy {
-    struct     imp;
-    imp *      m_imp;
-public:
-    der_strategy(ast_manager & m);
-    virtual ~der_strategy();
-
-    void operator()(assertion_set & s);
-    
-    virtual void operator()(assertion_set & s, model_converter_ref & mc) {
-        operator()(s);
-        mc = 0;
-    }
-
-    virtual void cleanup();
-    virtual void set_cancel(bool f);
-};
-
-inline as_st * mk_der(ast_manager & m) {
-    return alloc(der_strategy, m);
-}
-
-class tactic;
-
-tactic * mk_der_tactic(ast_manager & m);
-
 #endif /* _DER_H_ */
 
diff --git a/lib/expr_replacer.cpp b/src/rewriter/expr_replacer.cpp
similarity index 100%
rename from lib/expr_replacer.cpp
rename to src/rewriter/expr_replacer.cpp
diff --git a/lib/expr_replacer.h b/src/rewriter/expr_replacer.h
similarity index 100%
rename from lib/expr_replacer.h
rename to src/rewriter/expr_replacer.h
diff --git a/lib/push_app_ite.cpp b/src/simplifier/push_app_ite.cpp
similarity index 100%
rename from lib/push_app_ite.cpp
rename to src/simplifier/push_app_ite.cpp
diff --git a/lib/push_app_ite.h b/src/simplifier/push_app_ite.h
similarity index 100%
rename from lib/push_app_ite.h
rename to src/simplifier/push_app_ite.h
diff --git a/src/smt/smt_solver_strategy.cpp b/src/smt/smt_solver_strategy.cpp
new file mode 100644
index 000000000..65dde6361
--- /dev/null
+++ b/src/smt/smt_solver_strategy.cpp
@@ -0,0 +1,180 @@
+/*++
+Copyright (c) 2012 Microsoft Corporation
+
+Module Name:
+
+    smt_solver_strategy.cpp
+
+Abstract:
+
+    Wraps a solver as an assertion_set strategy.
+    **Temporary code**
+    It should be deleted when we finish porting the assertion_set code to the tactic framework.
+
+Author:
+
+    Leonardo (leonardo) 2012-10-20
+
+Notes:
+
+--*/
+#include"smt_solver_strategy.h"
+#include"smt_solver.h"
+
+class as_st_solver : public assertion_set_strategy {
+    scoped_ptr<front_end_params> m_params;
+    params_ref                   m_params_ref;
+    statistics                   m_stats;
+    std::string                  m_failure;
+    smt::solver *                m_ctx;
+    bool                         m_candidate_models;
+    symbol                       m_logic;
+    progress_callback *          m_callback;
+public:
+    as_st_solver(bool candidate_models):m_ctx(0), m_candidate_models(candidate_models), m_callback(0) {}
+    
+    front_end_params & fparams() {
+        if (!m_params)
+            m_params = alloc(front_end_params);
+        return *m_params;
+    }
+
+    struct scoped_init_ctx {
+        as_st_solver & m_owner;
+
+        scoped_init_ctx(as_st_solver & o, ast_manager & m):m_owner(o) {
+            smt::solver * new_ctx = alloc(smt::solver, m, o.fparams());
+            TRACE("as_solver", tout << "logic: " << o.m_logic << "\n";);
+            new_ctx->set_logic(o.m_logic);
+            if (o.m_callback) {
+                new_ctx->set_progress_callback(o.m_callback);
+            }
+            #pragma omp critical (as_st_solver) 
+            {
+                o.m_ctx = new_ctx;
+            }
+        }
+
+        ~scoped_init_ctx() {
+            smt::solver * d = m_owner.m_ctx;
+            #pragma omp critical (as_st_cancel)
+            {
+                m_owner.m_ctx = 0;
+            }
+            if (d)
+                dealloc(d);
+        }
+    };
+
+    virtual ~as_st_solver() {
+        SASSERT(m_ctx == 0);
+    }
+
+    virtual void updt_params(params_ref const & p) {
+        TRACE("as_solver", tout << "updt_params: " << p << "\n";);
+        m_params_ref = p;
+        params2front_end_params(m_params_ref, fparams());
+    }
+
+    virtual void collect_param_descrs(param_descrs & r) {
+    }
+
+    virtual void set_cancel(bool f) {
+        if (m_ctx)
+            m_ctx->set_cancel(f);
+    }
+
+    virtual void operator()(assertion_set & s, model_converter_ref & mc) {
+        SASSERT(is_well_sorted(s));
+        IF_VERBOSE(ST_VERBOSITY_LVL, verbose_stream() << "(smt-solver)" << std::endl;);
+        TRACE("as_solver", tout << "AUTO_CONFIG: " << fparams().m_auto_config << " HIDIV0: " << fparams().m_hi_div0 << " " 
+              << " PREPROCESS: " << fparams().m_preprocess << ", SOLVER:" << fparams().m_solver << "\n";);
+        TRACE("as_solver_detail", s.display(tout););        
+        ast_manager & m = s.m();
+        TRACE("as_solver_memory", tout << "wasted_size: " << m.get_allocator().get_wasted_size() << "\n";);        
+        // verbose_stream() << "wasted_size: " << m.get_allocator().get_wasted_size() << ", free_objs: " << m.get_allocator().get_num_free_objs() << "\n";
+        // m.get_allocator().consolidate();        
+        scoped_init_ctx  init(*this, m);
+        SASSERT(m_ctx != 0);
+        unsigned sz = s.size();
+        for (unsigned i = 0; i < sz; i++) {
+            expr * f = s.form(i);
+            m_ctx->assert_expr(f);
+        }
+        lbool r = m_ctx->setup_and_check();
+        m_ctx->collect_statistics(m_stats);
+        switch (r) {
+        case l_true: {
+            // the empty assertion set is trivially satifiable.
+            s.reset(); 
+            // store the model in a do nothin model converter.
+            model_ref md;
+            m_ctx->get_model(md);
+            mc = model2model_converter(md.get());
+            return;
+        }
+        case l_false:
+            // formula is unsat, reset the assertion set, and store false there.
+            s.reset();
+            s.assert_expr(m.mk_false(), m_ctx->get_proof());
+            return;
+        case l_undef:
+            if (m_candidate_models) {
+                switch (m_ctx->last_failure()) {
+                case smt::NUM_CONFLICTS:
+                case smt::THEORY:
+                case smt::QUANTIFIERS: {
+                    model_ref md;
+                    m_ctx->get_model(md);
+                    mc = model2model_converter(md.get());
+                    return;
+                }
+                default:
+                    break;
+                }
+            }
+            m_failure = m_ctx->last_failure_as_string();
+            throw strategy_exception(m_failure.c_str());
+        }
+    }
+
+    virtual void collect_statistics(statistics & st) const {
+        if (m_ctx)
+            m_ctx->collect_statistics(st); // ctx is still running...
+        else
+            st.copy(m_stats);
+    }
+
+    virtual void cleanup() {
+    }
+
+    virtual void reset_statistics() {
+        m_stats.reset();
+    }
+    
+    // for backward compatibility
+    virtual void set_front_end_params(front_end_params & p) {
+        m_params = alloc(front_end_params, p);
+        // must propagate the params_ref to fparams
+        params2front_end_params(m_params_ref, fparams());
+    }
+
+    virtual void set_logic(symbol const & l) {
+        m_logic = l;
+    }
+
+    virtual void set_progress_callback(progress_callback * callback) {
+        m_callback = callback;
+    }
+};
+
+as_st * mk_smt_solver_core(bool candidate_models) {
+    return alloc(as_st_solver, candidate_models);
+}
+
+as_st * mk_smt_solver(bool auto_config, bool candidate_models) {
+    as_st * solver = mk_smt_solver_core(candidate_models);
+    params_ref solver_p;    
+    solver_p.set_bool(":auto-config", auto_config);
+    return using_params(solver, solver_p);
+};
diff --git a/src/smt/smt_solver_strategy.h b/src/smt/smt_solver_strategy.h
new file mode 100644
index 000000000..eb74dc530
--- /dev/null
+++ b/src/smt/smt_solver_strategy.h
@@ -0,0 +1,31 @@
+/*++
+Copyright (c) 2012 Microsoft Corporation
+
+Module Name:
+
+    smt_solver_strategy.h
+
+Abstract:
+
+    Wraps a solver as an assertion_set strategy.
+    **Temporary code**
+    It should be deleted when we finish porting the assertion_set code to the tactic framework.
+
+Author:
+
+    Leonardo (leonardo) 2012-10-20
+
+Notes:
+
+--*/
+#ifndef _SMT_SOLVER_STRATEGY_H_
+#define _SMT_SOLVER_STRATEGY_H_
+
+#include"assertion_set_strategy.h"
+
+as_st * mk_smt_solver_core(bool candidate_models = false);
+as_st * mk_smt_solver(bool auto_config = true, bool candidate_models = false);
+
+MK_SIMPLE_ST_FACTORY(smt_solver_stf, mk_smt_solver());
+
+#endif
diff --git a/src/spc/README b/src/spc/README
new file mode 100644
index 000000000..67ccf0e3c
--- /dev/null
+++ b/src/spc/README
@@ -0,0 +1,2 @@
+Superposition Calculus.
+This module is currently disabled.
\ No newline at end of file
diff --git a/lib/expr_offset.h b/src/spc/expr_offset.h
similarity index 100%
rename from lib/expr_offset.h
rename to src/spc/expr_offset.h
diff --git a/lib/expr_offset_map.h b/src/spc/expr_offset_map.h
similarity index 100%
rename from lib/expr_offset_map.h
rename to src/spc/expr_offset_map.h
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