adding drat

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

src/sat/sat_drat.h

@@ -0,0 +1,41 @@
+/*++
+Copyright (c) 2014 Microsoft Corporation
+
+Module Name:
+
+    sat_drat.h
+
+Abstract:
+   
+    Produce DRAT proofs.
+
+Author:
+
+    Nikolaj Bjorner (nbjorner) 2017-2-3
+
+Notes:
+
+--*/
+#ifndef SAT_DRAT_H_
+#define SAT_DRAT_H_
+
+namespace sat {
+    class drat {
+        solver& s;
+        std::ostream* m_out;
+    public:
+        drat(solver& s);
+        ~drat();  
+        void add_empty();
+        void add_literal(literal l);
+        void add_binary(literal l1, literal l2);
+        void add_ternary(literal l1, literal l2, literal l3);
+        void add_clause(clause& c);
+        void del_literal(literal l);
+        void del_binary(literal l1, literal l2);
+        void del_clause(clause& c);
+    };
+
+};
+
+#endif