diff --git a/src/api/api_solver.cpp b/src/api/api_solver.cpp
index 8f92d5bb4..330d0f2bc 100644
--- a/src/api/api_solver.cpp
+++ b/src/api/api_solver.cpp
@@ -163,12 +163,46 @@ extern "C" {
         to_solver_ref(s)->set_model_converter(ctx->get_model_converter());
     }
 
+    static void solver_from_dimacs_stream(Z3_context c, Z3_solver s, std::istream& is) {
+        init_solver(c, s);
+        ast_manager& m = to_solver_ref(s)->get_manager();
+        std::stringstream err;
+        sat::solver solver(to_solver_ref(s)->get_params(), m.limit());
+        if (!parse_dimacs(is, err, solver)) {
+            SET_ERROR_CODE(Z3_PARSER_ERROR, err.str().c_str());
+            return;
+        }
+        sat2goal s2g;
+        ref<sat2goal::mc> mc;
+        atom2bool_var a2b(m);
+        for (unsigned v = 0; v < solver.num_vars(); ++v) {
+            a2b.insert(m.mk_const(symbol(v), m.mk_bool_sort()), v);
+        }
+        goal g(m);            
+        s2g(solver, a2b, to_solver_ref(s)->get_params(), g, mc);
+        for (unsigned i = 0; i < g.size(); ++i) {
+            to_solver_ref(s)->assert_expr(g.form(i));
+        }
+    }
+
+    // DIMACS files start with "p cnf" and number of variables/clauses.
+    // This is not legal SMT syntax, so use the DIMACS parser.
+    static bool is_dimacs_string(Z3_string c_str) {
+        std::cout << c_str << "\n";
+        return c_str[0] == 'p' && c_str[1] == ' ' && c_str[2] == 'c';
+    }
+
     void Z3_API Z3_solver_from_string(Z3_context c, Z3_solver s, Z3_string c_str) {
         Z3_TRY;
         LOG_Z3_solver_from_string(c, s, c_str);
         std::string str(c_str);
         std::istringstream is(str);
-        solver_from_stream(c, s, is);
+        if (is_dimacs_string(c_str)) {
+            solver_from_dimacs_stream(c, s, is);
+        }
+        else {
+            solver_from_stream(c, s, is);
+        }
         Z3_CATCH;        
     }
 
@@ -182,24 +216,7 @@ extern "C" {
             SET_ERROR_CODE(Z3_FILE_ACCESS_ERROR, nullptr);
         }
         else if (ext && (std::string("dimacs") == ext || std::string("cnf") == ext)) {
-            ast_manager& m = to_solver_ref(s)->get_manager();
-            std::stringstream err;
-            sat::solver solver(to_solver_ref(s)->get_params(), m.limit());
-            if (!parse_dimacs(is, err, solver)) {
-                SET_ERROR_CODE(Z3_PARSER_ERROR, err.str().c_str());
-                return;
-            }
-            sat2goal s2g;
-            ref<sat2goal::mc> mc;
-            atom2bool_var a2b(m);
-            for (unsigned v = 0; v < solver.num_vars(); ++v) {
-                a2b.insert(m.mk_const(symbol(v), m.mk_bool_sort()), v);
-            }
-            goal g(m);            
-            s2g(solver, a2b, to_solver_ref(s)->get_params(), g, mc);
-            for (unsigned i = 0; i < g.size(); ++i) {
-                to_solver_ref(s)->assert_expr(g.form(i));
-            }
+            solver_from_dimacs_stream(c, s, is);
         }
         else {
             solver_from_stream(c, s, is);
@@ -532,6 +549,17 @@ extern "C" {
         Z3_CATCH_RETURN("");
     }
 
+    Z3_string Z3_API Z3_solver_to_dimacs_string(Z3_context c, Z3_solver s) {
+        Z3_TRY;
+        LOG_Z3_solver_to_string(c, s);
+        RESET_ERROR_CODE();
+        init_solver(c, s);
+        std::ostringstream buffer;
+        to_solver_ref(s)->display_dimacs(buffer);
+        return mk_c(c)->mk_external_string(buffer.str());
+        Z3_CATCH_RETURN("");
+    }
+
 
     Z3_lbool Z3_API Z3_get_implied_equalities(Z3_context c, 
                                               Z3_solver s,
diff --git a/src/api/c++/z3++.h b/src/api/c++/z3++.h
index e541080c9..9847e4264 100644
--- a/src/api/c++/z3++.h
+++ b/src/api/c++/z3++.h
@@ -2240,6 +2240,8 @@ namespace z3 {
                                    fml));
         }
 
+        std::string dimacs() const { return std::string(Z3_solver_to_dimacs_string(ctx(), m_solver)); }
+
         param_descrs get_param_descrs() { return param_descrs(ctx(), Z3_solver_get_param_descrs(ctx(), m_solver)); }
 
 
diff --git a/src/api/python/z3/z3.py b/src/api/python/z3/z3.py
index 65f634b6b..1886bc475 100644
--- a/src/api/python/z3/z3.py
+++ b/src/api/python/z3/z3.py
@@ -6800,6 +6800,10 @@ class Solver(Z3PPObject):
         """
         return Z3_solver_to_string(self.ctx.ref(), self.solver)
 
+    def dimacs(self):
+        """Return a textual representation of the solver in DIMACS format."""
+        return Z3_solver_to_dimacs_string(self.ctx.ref(), self.solver)
+
     def to_smt2(self):
         """return SMTLIB2 formatted benchmark for solver's assertions"""
         es = self.assertions()
diff --git a/src/api/z3_api.h b/src/api/z3_api.h
index 5ee7fcb99..cd52d2d86 100644
--- a/src/api/z3_api.h
+++ b/src/api/z3_api.h
@@ -6368,6 +6368,14 @@ extern "C" {
     */
     Z3_string Z3_API Z3_solver_to_string(Z3_context c, Z3_solver s);
 
+    /**
+       \brief Convert a solver into a DIMACS formatted string.
+       \sa Z3_goal_to_diamcs_string for requirements.
+
+       def_API('Z3_solver_to_dimacs_string', STRING, (_in(CONTEXT), _in(SOLVER)))
+    */
+    Z3_string Z3_API Z3_solver_to_dimacs_string(Z3_context c, Z3_solver s);
+
     /*@}*/
 
     /** @name Statistics */
diff --git a/src/ast/CMakeLists.txt b/src/ast/CMakeLists.txt
index ce2817b58..56ab78b8a 100644
--- a/src/ast/CMakeLists.txt
+++ b/src/ast/CMakeLists.txt
@@ -17,6 +17,7 @@ z3_add_component(ast
     csp_decl_plugin.cpp
     datatype_decl_plugin.cpp
     decl_collector.cpp
+    display_dimacs.cpp
     dl_decl_plugin.cpp
     expr2polynomial.cpp
     expr2var.cpp
diff --git a/src/ast/display_dimacs.cpp b/src/ast/display_dimacs.cpp
new file mode 100644
index 000000000..da39538d9
--- /dev/null
+++ b/src/ast/display_dimacs.cpp
@@ -0,0 +1,81 @@
+/*++
+Copyright (c) 2019 Microsoft Corporation
+
+Module Name:
+
+    display_dimacs.h
+
+Abstract:
+
+    Display expressions in DIMACS format.
+    
+Author:
+
+    Nikolaj Bjorner (nbjorner0 2019-01-24
+
+Revision History:
+
+--*/
+
+#include "ast.h"
+#include "display_dimacs.h"
+
+std::ostream& display_dimacs(std::ostream& out, expr_ref_vector const& fmls) {
+    ast_manager& m = fmls.m();
+    unsigned_vector expr2var;
+    ptr_vector<expr> exprs;
+    unsigned num_vars = 0;
+    unsigned num_cls  = fmls.size();
+    for (expr * f : fmls) {
+        unsigned num_lits;
+        expr * const * lits;
+        if (m.is_or(f)) {
+            num_lits = to_app(f)->get_num_args();
+            lits     = to_app(f)->get_args();
+        }
+        else {
+            num_lits = 1;
+            lits     = &f;
+        }
+        for (unsigned j = 0; j < num_lits; j++) {
+            expr * l = lits[j];
+            if (m.is_not(l))
+                l = to_app(l)->get_arg(0);
+            if (expr2var.get(l->get_id(), UINT_MAX) == UINT_MAX) {
+                num_vars++;
+                expr2var.setx(l->get_id(), num_vars, UINT_MAX);
+                exprs.setx(l->get_id(), l, nullptr);
+            }
+        }
+    }
+    out << "p cnf " << num_vars << " " << num_cls << "\n";
+    for (expr* f : fmls) {
+        unsigned num_lits;
+        expr * const * lits;
+        if (m.is_or(f)) {
+            num_lits = to_app(f)->get_num_args();
+            lits     = to_app(f)->get_args();
+        }
+        else {
+            num_lits = 1;
+            lits     = &f;
+        }
+        for (unsigned j = 0; j < num_lits; j++) {
+            expr * l = lits[j];
+            if (m.is_not(l)) {
+                out << "-";
+                l = to_app(l)->get_arg(0);
+            }
+            SASSERT(exprs[l->get_id()]);
+            out << expr2var[l->get_id()] << " ";
+        }
+        out << "0\n";
+    }
+    for (expr* e : exprs) {
+        if (e && is_app(e)) {
+            symbol const& n = to_app(e)->get_decl()->get_name();
+            out << "c " << expr2var[e->get_id()] << " " << n << "\n";            
+        }
+    }
+    return out;
+}
diff --git a/src/ast/display_dimacs.h b/src/ast/display_dimacs.h
new file mode 100644
index 000000000..91c2386be
--- /dev/null
+++ b/src/ast/display_dimacs.h
@@ -0,0 +1,26 @@
+/*++
+Copyright (c) 2019 Microsoft Corporation
+
+Module Name:
+
+    display_dimacs.h
+
+Abstract:
+
+    Display expressions in DIMACS format.
+    
+Author:
+
+    Nikolaj Bjorner (nbjorner0 2019-01-24
+
+Revision History:
+
+--*/
+#ifndef DISPLAY_DIMACS_H_
+#define DISPLAY_DIMACS_H_
+
+#include "ast.h"
+
+std::ostream& display_dimacs(std::ostream& out, expr_ref_vector const& fmls);
+
+#endif /* DISPLAY_DIMACS_H__ */
diff --git a/src/muz/spacer/spacer_iuc_solver.cpp b/src/muz/spacer/spacer_iuc_solver.cpp
index 32f33f773..f28864e27 100644
--- a/src/muz/spacer/spacer_iuc_solver.cpp
+++ b/src/muz/spacer/spacer_iuc_solver.cpp
@@ -27,443 +27,426 @@ Notes:
 #include "muz/spacer/spacer_iuc_proof.h"
 
 namespace spacer {
-void iuc_solver::push ()
-{
-    m_defs.push_back (def_manager (*this));
-    m_solver.push ();
-}
-
-void iuc_solver::pop (unsigned n)
-{
-    m_solver.pop (n);
-    unsigned lvl = m_defs.size ();
-    SASSERT (n <= lvl);
-    unsigned new_lvl = lvl-n;
-    while (m_defs.size() > new_lvl) {
-        m_num_proxies -= m_defs.back ().m_defs.size ();
-        m_defs.pop_back ();
+    void iuc_solver::push () {
+        m_defs.push_back (def_manager (*this));
+        m_solver.push ();
     }
-}
-
-app* iuc_solver::fresh_proxy ()
-{
-    if (m_num_proxies == m_proxies.size()) {
-        std::stringstream name;
-        name << "spacer_proxy!" << m_proxies.size ();
-        app_ref res(m);
-        res = m.mk_const (symbol (name.str ().c_str ()),
-                          m.mk_bool_sort ());
-        m_proxies.push_back (res);
-
-        // -- add the new proxy to proxy eliminator
-        proof_ref pr(m);
-        pr = m.mk_asserted (m.mk_true ());
-        m_elim_proxies_sub.insert (res, m.mk_true (), pr);
 
+    void iuc_solver::pop (unsigned n) {
+        m_solver.pop (n);
+        unsigned lvl = m_defs.size ();
+        SASSERT (n <= lvl);
+        unsigned new_lvl = lvl-n;
+        while (m_defs.size() > new_lvl) {
+            m_num_proxies -= m_defs.back ().m_defs.size ();
+            m_defs.pop_back ();
+        }
     }
-    return m_proxies.get (m_num_proxies++);
-}
 
-app* iuc_solver::mk_proxy (expr *v)
-{
-    {
+    app* iuc_solver::fresh_proxy () {
+        if (m_num_proxies == m_proxies.size()) {
+            std::stringstream name;
+            name << "spacer_proxy!" << m_proxies.size ();
+            app_ref res(m);
+            res = m.mk_const (symbol (name.str ().c_str ()),
+                              m.mk_bool_sort ());
+            m_proxies.push_back (res);
+            
+            // -- add the new proxy to proxy eliminator
+            proof_ref pr(m);
+            pr = m.mk_asserted (m.mk_true ());
+            m_elim_proxies_sub.insert (res, m.mk_true (), pr);
+            
+        }
+        return m_proxies.get (m_num_proxies++);
+    }
+
+    app* iuc_solver::mk_proxy (expr *v) {
         expr *e = v;
         m.is_not (v, e);
-        if (is_uninterp_const(e)) { return to_app(v); }
+        if (is_uninterp_const(e)) { 
+            return to_app(v); 
+        }
+            
+        def_manager &def = !m_defs.empty() ? m_defs.back () : m_base_defs;
+        return def.mk_proxy (v);
     }
 
-    def_manager &def = !m_defs.empty() ? m_defs.back () : m_base_defs;
-    return def.mk_proxy (v);
-}
-
-bool iuc_solver::mk_proxies (expr_ref_vector &v, unsigned from)
-{
-    bool dirty = false;
-    for (unsigned i = from, sz = v.size(); i < sz; ++i) {
-        app *p = mk_proxy (v.get (i));
-        dirty |= (v.get (i) != p);
-        v[i] = p;
+    bool iuc_solver::mk_proxies (expr_ref_vector &v, unsigned from) {
+        bool dirty = false;
+        for (unsigned i = from, sz = v.size(); i < sz; ++i) {
+            app *p = mk_proxy (v.get (i));
+            dirty |= (v.get (i) != p);
+            v[i] = p;
+        }
+        return dirty;
     }
-    return dirty;
-}
 
-void iuc_solver::push_bg (expr *e)
-{
-    if (m_assumptions.size () > m_first_assumption)
-    { m_assumptions.shrink(m_first_assumption); }
-    m_assumptions.push_back (e);
-    m_first_assumption = m_assumptions.size ();
-}
-
-void iuc_solver::pop_bg (unsigned n)
-{
-    if (n == 0) { return; }
-
-    if (m_assumptions.size () > m_first_assumption) {
+    void iuc_solver::push_bg (expr *e) {
+        if (m_assumptions.size () > m_first_assumption) { 
+            m_assumptions.shrink(m_first_assumption); 
+        }
+        m_assumptions.push_back (e);
+        m_first_assumption = m_assumptions.size ();
+    }
+    
+    void iuc_solver::pop_bg (unsigned n) {
+        if (n == 0) return;
+        
+        if (m_assumptions.size () > m_first_assumption) {
+            m_assumptions.shrink(m_first_assumption);
+        }
+        m_first_assumption = m_first_assumption > n ? m_first_assumption - n : 0;
+        m_assumptions.shrink (m_first_assumption);
+    }
+    
+    unsigned iuc_solver::get_num_bg () {
+        return m_first_assumption;
+    }
+    
+    lbool iuc_solver::check_sat_core (unsigned num_assumptions, expr * const *assumptions) {
+        // -- remove any old assumptions
         m_assumptions.shrink(m_first_assumption);
+        
+        // -- replace theory literals in background assumptions with proxies
+        mk_proxies (m_assumptions);
+        // -- in case mk_proxies added new literals, they are all background
+        m_first_assumption = m_assumptions.size ();
+        
+        m_assumptions.append (num_assumptions, assumptions);
+        m_is_proxied = mk_proxies (m_assumptions, m_first_assumption);
+        
+        return set_status (m_solver.check_sat (m_assumptions));
     }
-    m_first_assumption = m_first_assumption > n ? m_first_assumption - n : 0;
-    m_assumptions.shrink (m_first_assumption);
-}
+    
+    lbool iuc_solver::check_sat_cc(const expr_ref_vector &cube,
+                                   vector<expr_ref_vector> const & clauses) {
+        if (clauses.empty())
+            return check_sat(cube.size(), cube.c_ptr());
+        
+        // -- remove any old assumptions
+        m_assumptions.shrink(m_first_assumption);
+        
+        // -- replace theory literals in background assumptions with proxies
+        mk_proxies(m_assumptions);
+        // -- in case mk_proxies added new literals, they are all background
+        m_first_assumption = m_assumptions.size();
+        
+        m_assumptions.append(cube);
+        m_is_proxied = mk_proxies(m_assumptions, m_first_assumption);
+        
+        return set_status (m_solver.check_sat_cc(m_assumptions, clauses));
+    }
+    
 
-unsigned iuc_solver::get_num_bg () {return m_first_assumption;}
-
-lbool iuc_solver::check_sat (unsigned num_assumptions, expr * const *assumptions)
-{
-    // -- remove any old assumptions
-    m_assumptions.shrink(m_first_assumption);
-
-    // -- replace theory literals in background assumptions with proxies
-    mk_proxies (m_assumptions);
-    // -- in case mk_proxies added new literals, they are all background
-    m_first_assumption = m_assumptions.size ();
-
-    m_assumptions.append (num_assumptions, assumptions);
-    m_is_proxied = mk_proxies (m_assumptions, m_first_assumption);
-
-    return set_status (m_solver.check_sat (m_assumptions));
-}
-
-lbool iuc_solver::check_sat_cc(const expr_ref_vector &cube,
-                               vector<expr_ref_vector> const & clauses) {
-    if (clauses.empty())
-        return check_sat(cube.size(), cube.c_ptr());
-
-    // -- remove any old assumptions
-    m_assumptions.shrink(m_first_assumption);
-
-    // -- replace theory literals in background assumptions with proxies
-    mk_proxies(m_assumptions);
-    // -- in case mk_proxies added new literals, they are all background
-    m_first_assumption = m_assumptions.size();
-
-    m_assumptions.append(cube);
-    m_is_proxied = mk_proxies(m_assumptions, m_first_assumption);
-
-    return set_status (m_solver.check_sat_cc(m_assumptions, clauses));
-}
-
-
-app* iuc_solver::def_manager::mk_proxy (expr *v)
-{
-    app* r;
-    if (m_expr2proxy.find(v, r))
-        return r;
-
-    ast_manager &m = m_parent.m;
-    app* proxy = m_parent.fresh_proxy ();
-    app* def = m.mk_or (m.mk_not (proxy), v);
-    m_defs.push_back (def);
-    m_expr2proxy.insert (v, proxy);
-    m_proxy2def.insert (proxy, def);
-
-    m_parent.assert_expr (def);
-    return proxy;
-}
-
-bool iuc_solver::def_manager::is_proxy (app *k, app_ref &def)
-{
-    app *r = nullptr;
-    bool found = m_proxy2def.find (k, r);
-    def = r;
-    return found;
-}
-
-void iuc_solver::def_manager::reset ()
-{
-    m_expr2proxy.reset ();
-    m_proxy2def.reset ();
-    m_defs.reset ();
-}
-
-bool iuc_solver::def_manager::is_proxy_def (expr *v)
-{
-    // XXX This might not be the most robust way to check
-    return m_defs.contains (v);
-}
-
-bool iuc_solver::is_proxy(expr *e, app_ref &def)
-{
-    if (!is_uninterp_const(e))
-        return false;
-
-    app* a = to_app (e);
-
-    for (int i = m_defs.size (); i-- > 0; )
-        if (m_defs[i].is_proxy (a, def))
-            return true;
-
-    return m_base_defs.is_proxy (a, def);
-}
-
-void iuc_solver::collect_statistics (statistics &st) const
-{
-    m_solver.collect_statistics (st);
-    st.update ("time.iuc_solver.get_iuc", m_iuc_sw.get_seconds());
-    st.update ("time.iuc_solver.get_iuc.hyp_reduce1", m_hyp_reduce1_sw.get_seconds());
-    st.update ("time.iuc_solver.get_iuc.hyp_reduce2", m_hyp_reduce2_sw.get_seconds());
-    st.update ("time.iuc_solver.get_iuc.learn_core", m_learn_core_sw.get_seconds());
-
-    st.update("iuc_solver.num_proxies", m_proxies.size());
-}
-
-void iuc_solver::reset_statistics ()
-{
-    m_iuc_sw.reset();
-    m_hyp_reduce1_sw.reset();
-    m_hyp_reduce2_sw.reset();
-    m_learn_core_sw.reset();
-}
-
-void iuc_solver::get_unsat_core (expr_ref_vector &core) {
-    m_solver.get_unsat_core (core);
-    undo_proxies_in_core (core);
-}
-
-void iuc_solver::undo_proxies_in_core (expr_ref_vector &r)
-{
-    app_ref e(m);
-    expr_fast_mark1 bg;
-    for (unsigned i = 0; i < m_first_assumption; ++i) {
-        bg.mark(m_assumptions.get(i));
+    app* iuc_solver::def_manager::mk_proxy (expr *v) {
+        app* r;
+        if (m_expr2proxy.find(v, r))
+            return r;
+        
+        ast_manager &m = m_parent.m;
+        app* proxy = m_parent.fresh_proxy ();
+        app* def = m.mk_or (m.mk_not (proxy), v);
+        m_defs.push_back (def);
+        m_expr2proxy.insert (v, proxy);
+        m_proxy2def.insert (proxy, def);
+        
+        m_parent.assert_expr (def);
+        return proxy;
     }
 
-    // expand proxies
-    unsigned j = 0;
-    for (expr* rr : r) {
-        // skip background assumptions
-        if (bg.is_marked(rr))
-            continue;
+    bool iuc_solver::def_manager::is_proxy (app *k, app_ref &def) {
+        app *r = nullptr;
+        bool found = m_proxy2def.find (k, r);
+        def = r;
+        return found;
+    }
+    
+    void iuc_solver::def_manager::reset () {
+        m_expr2proxy.reset ();
+        m_proxy2def.reset ();
+        m_defs.reset ();
+    }
 
-        // -- undo proxies, but only if they were introduced in check_sat
-        if (m_is_proxied && is_proxy(rr, e)) {
-            SASSERT (m.is_or (e));
-            r[j++] = e->get_arg (1);
+    bool iuc_solver::def_manager::is_proxy_def (expr *v) {
+        // XXX This might not be the most robust way to check
+        return m_defs.contains (v);
+    }
+
+    bool iuc_solver::is_proxy(expr *e, app_ref &def) {
+        if (!is_uninterp_const(e))
+            return false;
+        
+        app* a = to_app (e);
+        
+        for (int i = m_defs.size (); i-- > 0; )
+            if (m_defs[i].is_proxy (a, def))
+                return true;
+        
+        return m_base_defs.is_proxy (a, def);
+    }
+
+    void iuc_solver::collect_statistics (statistics &st) const {
+        m_solver.collect_statistics (st);
+        st.update ("time.iuc_solver.get_iuc", m_iuc_sw.get_seconds());
+        st.update ("time.iuc_solver.get_iuc.hyp_reduce1", m_hyp_reduce1_sw.get_seconds());
+        st.update ("time.iuc_solver.get_iuc.hyp_reduce2", m_hyp_reduce2_sw.get_seconds());
+        st.update ("time.iuc_solver.get_iuc.learn_core", m_learn_core_sw.get_seconds());
+        
+        st.update("iuc_solver.num_proxies", m_proxies.size());
+    }
+    
+    void iuc_solver::reset_statistics () {
+        m_iuc_sw.reset();
+        m_hyp_reduce1_sw.reset();
+        m_hyp_reduce2_sw.reset();
+        m_learn_core_sw.reset();
+    }
+    
+    void iuc_solver::get_unsat_core (expr_ref_vector &core) {
+        m_solver.get_unsat_core (core);
+        undo_proxies_in_core (core);
+    }
+
+    void iuc_solver::undo_proxies_in_core (expr_ref_vector &r) {
+        app_ref e(m);
+        expr_fast_mark1 bg;
+        for (unsigned i = 0; i < m_first_assumption; ++i) {
+            bg.mark(m_assumptions.get(i));
+        }
+        
+        // expand proxies
+        unsigned j = 0;
+        for (expr* rr : r) {
+            // skip background assumptions
+            if (bg.is_marked(rr))
+                continue;
+            
+            // -- undo proxies, but only if they were introduced in check_sat
+            if (m_is_proxied && is_proxy(rr, e)) {
+                SASSERT (m.is_or (e));
+                r[j++] = e->get_arg (1);
+            }
+            else {
+                r[j++] = rr;
+            }
+        }
+        r.shrink (j);
+    }
+    
+    void iuc_solver::undo_proxies (expr_ref_vector &r) {
+        app_ref e(m);
+        // expand proxies
+        for (unsigned i = 0, sz = r.size (); i < sz; ++i)
+            if (is_proxy(r.get(i), e)) {
+                SASSERT (m.is_or (e));
+                r[i] = e->get_arg (1);
+            }
+    }
+    
+    void iuc_solver::elim_proxies (expr_ref_vector &v) {
+        expr_ref f = mk_and (v);
+        scoped_ptr<expr_replacer> rep = mk_expr_simp_replacer (m);
+        rep->set_substitution (&m_elim_proxies_sub);
+        (*rep)(f);
+        v.reset();
+        flatten_and(f, v);
+    }
+    
+    void iuc_solver::get_iuc(expr_ref_vector &core) {
+        scoped_watch _t_ (m_iuc_sw);
+        
+        typedef obj_hashtable<expr> expr_set;
+        expr_set core_lits;
+        for (unsigned i = m_first_assumption, sz = m_assumptions.size(); i < sz; ++i) {
+            expr *a = m_assumptions.get (i);
+            app_ref def(m);
+            if (is_proxy(a, def)) { core_lits.insert(def.get()); }
+            core_lits.insert (a);
+        }
+        
+        if (m_iuc == 0) {
+            // ORIGINAL PDR CODE
+            // AG: deprecated
+            proof_ref pr(m);
+            pr = get_proof ();
+            
+            farkas_learner learner_old;
+            learner_old.set_split_literals(m_split_literals);
+            
+            learner_old.get_lemmas (pr, core_lits, core);
+            elim_proxies (core);
+            simplify_bounds (core); // XXX potentially redundant
         }
         else {
-            r[j++] = rr;
-        }
-    }
-    r.shrink (j);
-}
-
-void iuc_solver::undo_proxies (expr_ref_vector &r)
-{
-    app_ref e(m);
-    // expand proxies
-    for (unsigned i = 0, sz = r.size (); i < sz; ++i)
-        if (is_proxy(r.get(i), e)) {
-            SASSERT (m.is_or (e));
-            r[i] = e->get_arg (1);
-        }
-}
-
-void iuc_solver::elim_proxies (expr_ref_vector &v)
-{
-    expr_ref f = mk_and (v);
-    scoped_ptr<expr_replacer> rep = mk_expr_simp_replacer (m);
-    rep->set_substitution (&m_elim_proxies_sub);
-    (*rep)(f);
-    v.reset();
-    flatten_and(f, v);
-}
-
-void iuc_solver::get_iuc(expr_ref_vector &core)
-{
-    scoped_watch _t_ (m_iuc_sw);
-
-    typedef obj_hashtable<expr> expr_set;
-    expr_set core_lits;
-    for (unsigned i = m_first_assumption, sz = m_assumptions.size(); i < sz; ++i) {
-        expr *a = m_assumptions.get (i);
-        app_ref def(m);
-        if (is_proxy(a, def)) { core_lits.insert(def.get()); }
-        core_lits.insert (a);
-    }
-
-    if (m_iuc == 0) {
-        // ORIGINAL PDR CODE
-        // AG: deprecated
-        proof_ref pr(m);
-        pr = get_proof ();
-
-        farkas_learner learner_old;
-        learner_old.set_split_literals(m_split_literals);
-
-        learner_old.get_lemmas (pr, core_lits, core);
-        elim_proxies (core);
-        simplify_bounds (core); // XXX potentially redundant
-    }
-    else {
-        // NEW IUC
-        proof_ref res(get_proof(), m);
-
-        // -- old hypothesis reducer while the new one is broken
-        if (m_old_hyp_reducer) {
-            scoped_watch _t_ (m_hyp_reduce1_sw);
-            // AG: deprecated
-            // pre-process proof in order to get a proof which is
-            // better suited for unsat-core-extraction
-            if (m_print_farkas_stats) {
-                iuc_proof iuc_before(m, res.get(), core_lits);
-                verbose_stream() << "\nOld reduce_hypotheses. Before:";
-                iuc_before.dump_farkas_stats();
+            // NEW IUC
+            proof_ref res(get_proof(), m);
+            
+            // -- old hypothesis reducer while the new one is broken
+            if (m_old_hyp_reducer) {
+                scoped_watch _t_ (m_hyp_reduce1_sw);
+                // AG: deprecated
+                // pre-process proof in order to get a proof which is
+                // better suited for unsat-core-extraction
+                if (m_print_farkas_stats) {
+                    iuc_proof iuc_before(m, res.get(), core_lits);
+                    verbose_stream() << "\nOld reduce_hypotheses. Before:";
+                    iuc_before.dump_farkas_stats();
+                }
+                
+                proof_utils::reduce_hypotheses(res);
+                proof_utils::permute_unit_resolution(res);
+                
+                if (m_print_farkas_stats) {
+                    iuc_proof iuc_after(m, res.get(), core_lits);
+                    verbose_stream() << "Old reduce_hypothesis. After:";
+                    iuc_after.dump_farkas_stats();
+                }
             }
-
-            proof_utils::reduce_hypotheses(res);
-            proof_utils::permute_unit_resolution(res);
-
-            if (m_print_farkas_stats) {
-                iuc_proof iuc_after(m, res.get(), core_lits);
-                verbose_stream() << "Old reduce_hypothesis. After:";
-                iuc_after.dump_farkas_stats();
-            }
-        }
-        // -- new hypothesis reducer
-        else
-        {
+            // -- new hypothesis reducer
+            else
+                {
 #if 0
-            static unsigned bcnt = 0;
+                    static unsigned bcnt = 0;
+                    {
+                        bcnt++;
+                        TRACE("spacer", tout << "Dumping pf bcnt: " << bcnt << "\n";);
+                        if (bcnt == 123) {
+                            std::ofstream ofs;
+                            ofs.open("/tmp/bpf_" + std::to_string(bcnt) + ".dot");
+                            iuc_proof iuc_pf_before(m, res.get(), core_lits);
+                            iuc_pf_before.display_dot(ofs);
+                            ofs.close();
+                            
+                            proof_checker pc(m);
+                            expr_ref_vector side(m);
+                            ENSURE(pc.check(res, side));
+                        }
+                    }
+#endif
+                    scoped_watch _t_ (m_hyp_reduce2_sw);
+                    
+                    // pre-process proof for better iuc extraction
+                    if (m_print_farkas_stats) {
+                        iuc_proof iuc_before(m, res.get(), core_lits);
+                        verbose_stream() << "\n New hypothesis_reducer. Before:";
+                        iuc_before.dump_farkas_stats();
+                    }
+                    
+                    proof_ref pr1(m);
+                    {
+                        scoped_watch _t_ (m_hyp_reduce1_sw);
+                        theory_axiom_reducer ta_reducer(m);
+                        pr1 = ta_reducer.reduce (res.get());
+                    }
+                    
+                    proof_ref pr2(m);
+                    {
+                        scoped_watch _t_ (m_hyp_reduce2_sw);
+                        hypothesis_reducer hyp_reducer(m);
+                        pr2 = hyp_reducer.reduce(pr1);
+                    }
+                    
+                    res = pr2;
+                    
+                    if (m_print_farkas_stats) {
+                        iuc_proof iuc_after(m, res.get(), core_lits);
+                        verbose_stream() << "New hypothesis_reducer. After:";
+                        iuc_after.dump_farkas_stats();
+                    }
+                }
+            
+            iuc_proof iuc_pf(m, res, core_lits);
+            
+#if 0
+            static unsigned cnt = 0;
             {
-                bcnt++;
-                TRACE("spacer", tout << "Dumping pf bcnt: " << bcnt << "\n";);
-                if (bcnt == 123) {
+                cnt++;
+                TRACE("spacer", tout << "Dumping pf cnt: " << cnt << "\n";);
+                if (cnt == 123) {
                     std::ofstream ofs;
-                    ofs.open("/tmp/bpf_" + std::to_string(bcnt) + ".dot");
-                    iuc_proof iuc_pf_before(m, res.get(), core_lits);
-                    iuc_pf_before.display_dot(ofs);
+                    ofs.open("/tmp/pf_" + std::to_string(cnt) + ".dot");
+                    iuc_pf.display_dot(ofs);
                     ofs.close();
-
                     proof_checker pc(m);
                     expr_ref_vector side(m);
                     ENSURE(pc.check(res, side));
                 }
             }
 #endif
-            scoped_watch _t_ (m_hyp_reduce2_sw);
-
-            // pre-process proof for better iuc extraction
-            if (m_print_farkas_stats) {
-                iuc_proof iuc_before(m, res.get(), core_lits);
-                verbose_stream() << "\n New hypothesis_reducer. Before:";
-                iuc_before.dump_farkas_stats();
+            unsat_core_learner learner(m, iuc_pf);
+            
+            unsat_core_plugin* plugin;
+            // -- register iuc plugins
+            switch (m_iuc_arith) {
+            case 0:
+            case 1:
+                plugin =
+                    alloc(unsat_core_plugin_farkas_lemma,
+                          learner, m_split_literals,
+                          (m_iuc_arith == 1) /* use constants from A */);
+                learner.register_plugin(plugin);
+                break;
+            case 2:
+                SASSERT(false && "Broken");
+                plugin = alloc(unsat_core_plugin_farkas_lemma_optimized, learner, m);
+                learner.register_plugin(plugin);
+                break;
+            case 3:
+                plugin = alloc(unsat_core_plugin_farkas_lemma_bounded, learner, m);
+                learner.register_plugin(plugin);
+                break;
+            default:
+                UNREACHABLE();
+                break;
             }
-
-            proof_ref pr1(m);
+            
+            switch (m_iuc) {
+            case 1:
+                // -- iuc based on the lowest cut in the proof
+                plugin = alloc(unsat_core_plugin_lemma, learner);
+                learner.register_plugin(plugin);
+                break;
+            case 2:
+                // -- iuc based on the smallest cut in the proof
+                plugin = alloc(unsat_core_plugin_min_cut, learner, m);
+                learner.register_plugin(plugin);
+                break;
+            default:
+                UNREACHABLE();
+                break;
+            }
+            
             {
-                scoped_watch _t_ (m_hyp_reduce1_sw);
-                theory_axiom_reducer ta_reducer(m);
-                pr1 = ta_reducer.reduce (res.get());
-            }
-
-            proof_ref pr2(m);
-            {
-                scoped_watch _t_ (m_hyp_reduce2_sw);
-                hypothesis_reducer hyp_reducer(m);
-                pr2 = hyp_reducer.reduce(pr1);
-            }
-
-            res = pr2;
-
-            if (m_print_farkas_stats) {
-                iuc_proof iuc_after(m, res.get(), core_lits);
-                verbose_stream() << "New hypothesis_reducer. After:";
-                iuc_after.dump_farkas_stats();
+                scoped_watch _t_ (m_learn_core_sw);
+                // compute interpolating unsat core
+                learner.compute_unsat_core(core);
             }
+            
+            elim_proxies (core);
+            // AG: this should be taken care of by minimizing the iuc cut
+            simplify_bounds (core);
         }
-
-        iuc_proof iuc_pf(m, res, core_lits);
-
-#if 0
-        static unsigned cnt = 0;
-        {
-            cnt++;
-            TRACE("spacer", tout << "Dumping pf cnt: " << cnt << "\n";);
-            if (cnt == 123) {
-                std::ofstream ofs;
-                ofs.open("/tmp/pf_" + std::to_string(cnt) + ".dot");
-                iuc_pf.display_dot(ofs);
-                ofs.close();
-                proof_checker pc(m);
-                expr_ref_vector side(m);
-                ENSURE(pc.check(res, side));
-            }
-        }
-#endif
-        unsat_core_learner learner(m, iuc_pf);
-
-        unsat_core_plugin* plugin;
-        // -- register iuc plugins
-        switch (m_iuc_arith) {
-        case 0:
-        case 1:
-            plugin =
-                alloc(unsat_core_plugin_farkas_lemma,
-                      learner, m_split_literals,
-                      (m_iuc_arith == 1) /* use constants from A */);
-            learner.register_plugin(plugin);
-            break;
-        case 2:
-            SASSERT(false && "Broken");
-            plugin = alloc(unsat_core_plugin_farkas_lemma_optimized, learner, m);
-            learner.register_plugin(plugin);
-            break;
-        case 3:
-            plugin = alloc(unsat_core_plugin_farkas_lemma_bounded, learner, m);
-            learner.register_plugin(plugin);
-            break;
-        default:
-            UNREACHABLE();
-            break;
-        }
-
-        switch (m_iuc) {
-        case 1:
-            // -- iuc based on the lowest cut in the proof
-            plugin = alloc(unsat_core_plugin_lemma, learner);
-            learner.register_plugin(plugin);
-            break;
-        case 2:
-            // -- iuc based on the smallest cut in the proof
-            plugin = alloc(unsat_core_plugin_min_cut, learner, m);
-            learner.register_plugin(plugin);
-            break;
-        default:
-            UNREACHABLE();
-            break;
-        }
-
-        {
-            scoped_watch _t_ (m_learn_core_sw);
-            // compute interpolating unsat core
-            learner.compute_unsat_core(core);
-        }
-
-        elim_proxies (core);
-        // AG: this should be taken care of by minimizing the iuc cut
-        simplify_bounds (core);
+        
+        IF_VERBOSE(2,
+                   verbose_stream () << "IUC Core:\n" << core << "\n";);
     }
-
-    IF_VERBOSE(2,
-               verbose_stream () << "IUC Core:\n" << core << "\n";);
-}
-
-void iuc_solver::refresh ()
-{
-    // only refresh in non-pushed state
-    SASSERT (m_defs.empty());
-    expr_ref_vector assertions (m);
-    for (unsigned i = 0, e = m_solver.get_num_assertions(); i < e; ++i) {
-        expr* a = m_solver.get_assertion (i);
-        if (!m_base_defs.is_proxy_def(a)) { assertions.push_back(a); }
-
+    
+    void iuc_solver::refresh () {
+        // only refresh in non-pushed state
+        SASSERT (m_defs.empty());
+        expr_ref_vector assertions (m);
+        for (unsigned i = 0, e = m_solver.get_num_assertions(); i < e; ++i) {
+            expr* a = m_solver.get_assertion (i);
+            if (!m_base_defs.is_proxy_def(a)) { assertions.push_back(a); }
+            
+        }
+        m_base_defs.reset ();
+        NOT_IMPLEMENTED_YET ();
+        // solver interface does not have a reset method. need to introduce it somewhere.
+        // m_solver.reset ();
+        for (unsigned i = 0, e = assertions.size (); i < e; ++i)
+            { m_solver.assert_expr(assertions.get(i)); }
     }
-    m_base_defs.reset ();
-    NOT_IMPLEMENTED_YET ();
-    // solver interface does not have a reset method. need to introduce it somewhere.
-    // m_solver.reset ();
-    for (unsigned i = 0, e = assertions.size (); i < e; ++i)
-    { m_solver.assert_expr(assertions.get(i)); }
-}
-
+    
 }
diff --git a/src/muz/spacer/spacer_iuc_solver.h b/src/muz/spacer/spacer_iuc_solver.h
index c0a0072ed..a51bfbef9 100644
--- a/src/muz/spacer/spacer_iuc_solver.h
+++ b/src/muz/spacer/spacer_iuc_solver.h
@@ -127,7 +127,7 @@ public:
     void pop(unsigned n) override;
     unsigned get_scope_level() const override { return m_solver.get_scope_level(); }
 
-    lbool check_sat(unsigned num_assumptions, expr * const *assumptions) override;
+    lbool check_sat_core(unsigned num_assumptions, expr * const *assumptions) override;
     lbool check_sat_cc(const expr_ref_vector &cube, vector<expr_ref_vector> const & clauses) override;
     void set_progress_callback(progress_callback *callback) override {
         m_solver.set_progress_callback(callback);
diff --git a/src/opt/opt_solver.cpp b/src/opt/opt_solver.cpp
index e61a02d80..78851f5cb 100644
--- a/src/opt/opt_solver.cpp
+++ b/src/opt/opt_solver.cpp
@@ -158,7 +158,7 @@ namespace opt {
         return m_dump_benchmarks;
     }
 
-    lbool opt_solver::check_sat_core(unsigned num_assumptions, expr * const * assumptions) {
+    lbool opt_solver::check_sat_core2(unsigned num_assumptions, expr * const * assumptions) {
         TRACE("opt_verbose", {
             tout << "context size: " << m_context.size() << "\n";            
             for (unsigned i = 0; i < m_context.size(); ++i) {
diff --git a/src/opt/opt_solver.h b/src/opt/opt_solver.h
index 39562ec54..8d2abdb93 100644
--- a/src/opt/opt_solver.h
+++ b/src/opt/opt_solver.h
@@ -95,7 +95,7 @@ namespace opt {
         void assert_expr_core(expr * t) override;
         void push_core() override;
         void pop_core(unsigned n) override;
-        lbool check_sat_core(unsigned num_assumptions, expr * const * assumptions) override;
+        lbool check_sat_core2(unsigned num_assumptions, expr * const * assumptions) override;
         void get_unsat_core(expr_ref_vector & r) override;
         void get_model_core(model_ref & _m) override;
         proof * get_proof() override;
diff --git a/src/sat/sat_solver/inc_sat_solver.cpp b/src/sat/sat_solver/inc_sat_solver.cpp
index 8823c40c5..34348f0fc 100644
--- a/src/sat/sat_solver/inc_sat_solver.cpp
+++ b/src/sat/sat_solver/inc_sat_solver.cpp
@@ -166,7 +166,7 @@ public:
             (m.is_not(e, e) && is_uninterp_const(e));
     }
 
-    lbool check_sat(unsigned sz, expr * const * assumptions) override {
+    lbool check_sat_core(unsigned sz, expr * const * assumptions) override {
         m_solver.pop_to_base_level();
         m_core.reset();
         if (m_solver.inconsistent()) return l_false;
diff --git a/src/smt/smt_solver.cpp b/src/smt/smt_solver.cpp
index 48f6053fc..5d32d1bed 100644
--- a/src/smt/smt_solver.cpp
+++ b/src/smt/smt_solver.cpp
@@ -185,7 +185,7 @@ namespace smt {
             m_context.pop(n);
         }
 
-        lbool check_sat_core(unsigned num_assumptions, expr * const * assumptions) override {
+        lbool check_sat_core2(unsigned num_assumptions, expr * const * assumptions) override {
             TRACE("solver_na2as", tout << "smt_solver::check_sat_core: " << num_assumptions << "\n";);
             return m_context.check(num_assumptions, assumptions);
         }
diff --git a/src/solver/CMakeLists.txt b/src/solver/CMakeLists.txt
index c8e206f7f..281a34018 100644
--- a/src/solver/CMakeLists.txt
+++ b/src/solver/CMakeLists.txt
@@ -16,5 +16,7 @@ z3_add_component(solver
   PYG_FILES
     combined_solver_params.pyg
     parallel_params.pyg
+  PYG_FILES
+    solver_params.pyg
 
 )
diff --git a/src/solver/combined_solver.cpp b/src/solver/combined_solver.cpp
index e8fb34815..813b2be18 100644
--- a/src/solver/combined_solver.cpp
+++ b/src/solver/combined_solver.cpp
@@ -218,7 +218,7 @@ public:
         return l_undef;
     }
 
-    lbool check_sat(unsigned num_assumptions, expr * const * assumptions) override {
+    lbool check_sat_core(unsigned num_assumptions, expr * const * assumptions) override {
         m_check_sat_executed  = true;        
         m_use_solver1_results = false;
 
@@ -227,13 +227,13 @@ public:
             m_ignore_solver1)  {
             // must use incremental solver
             switch_inc_mode();
-            return m_solver2->check_sat(num_assumptions, assumptions);
+            return m_solver2->check_sat_core(num_assumptions, assumptions);
         }
         
         if (m_inc_mode) {
             if (m_inc_timeout == UINT_MAX) {
                 IF_VERBOSE(PS_VB_LVL, verbose_stream() << "(combined-solver \"using solver 2 (without a timeout)\")\n";);            
-                lbool r = m_solver2->check_sat(num_assumptions, assumptions);
+                lbool r = m_solver2->check_sat_core(num_assumptions, assumptions);
                 if (r != l_undef || !use_solver1_when_undef() || get_manager().canceled()) {
                     return r;
                 }
@@ -244,7 +244,7 @@ public:
                 lbool r = l_undef;
                 try {
                     scoped_timer timer(m_inc_timeout, &eh);
-                    r = m_solver2->check_sat(num_assumptions, assumptions);
+                    r = m_solver2->check_sat_core(num_assumptions, assumptions);
                 }
                 catch (z3_exception&) {
                     if (!eh.m_canceled) {
@@ -260,7 +260,7 @@ public:
         
         IF_VERBOSE(PS_VB_LVL, verbose_stream() << "(combined-solver \"using solver 1\")\n";);
         m_use_solver1_results = true;
-        return m_solver1->check_sat(num_assumptions, assumptions);
+        return m_solver1->check_sat_core(num_assumptions, assumptions);
     }
     
     void set_progress_callback(progress_callback * callback) override {
diff --git a/src/solver/solver.cpp b/src/solver/solver.cpp
index f3c533704..6f4880d38 100644
--- a/src/solver/solver.cpp
+++ b/src/solver/solver.cpp
@@ -3,7 +3,7 @@ Copyright (c) 2011 Microsoft Corporation
 
 Module Name:
 
-    solver.h
+    solver.cpp
 
 Abstract:
 
@@ -21,25 +21,25 @@ Notes:
 #include "ast/ast_util.h"
 #include "ast/ast_pp.h"
 #include "ast/ast_pp_util.h"
+#include "ast/display_dimacs.h"
 #include "tactic/model_converter.h"
 #include "solver/solver.h"
+#include "solver/solver_params.hpp"
 #include "model/model_evaluator.h"
 
 
 unsigned solver::get_num_assertions() const {
-    NOT_IMPLEMENTED_YET();
+    UNREACHABLE();
     return 0;
 }
 
 expr * solver::get_assertion(unsigned idx) const {
-    NOT_IMPLEMENTED_YET();
+    UNREACHABLE();
     return nullptr;
 }
 
 std::ostream& solver::display(std::ostream & out, unsigned n, expr* const* assumptions) const {
     expr_ref_vector fmls(get_manager());
-    stopwatch sw;
-    sw.start();
     get_assertions(fmls);    
     ast_pp_util visitor(get_manager());
     model_converter_ref mc = get_model_converter();
@@ -57,6 +57,12 @@ std::ostream& solver::display(std::ostream & out, unsigned n, expr* const* assum
     return out;
 }
 
+std::ostream& solver::display_dimacs(std::ostream& out) const {
+    expr_ref_vector fmls(get_manager());
+    get_assertions(fmls);    
+    return ::display_dimacs(out, fmls);
+}
+
 void solver::get_assertions(expr_ref_vector& fmls) const {
     unsigned sz = get_num_assertions();
     for (unsigned i = 0; i < sz; ++i) {
@@ -232,12 +238,16 @@ void solver::collect_param_descrs(param_descrs & r) {
 
 void solver::reset_params(params_ref const & p) {
     m_params = p;
-    m_enforce_model_conversion = m_params.get_bool("solver.enforce_model_conversion", false);
+    solver_params sp(m_params);
+    m_enforce_model_conversion = sp.enforce_model_conversion();
+    m_cancel_backup_file = sp.cancel_backup_file();
 }
 
 void solver::updt_params(params_ref const & p) {
     m_params.copy(p);
-    m_enforce_model_conversion = m_params.get_bool("solver.enforce_model_conversion", false);
+    solver_params sp(m_params);
+    m_enforce_model_conversion = sp.enforce_model_conversion();
+    m_cancel_backup_file = sp.cancel_backup_file();
 }
 
 
@@ -309,3 +319,28 @@ expr_ref_vector solver::get_non_units(ast_manager& m) {
     }
     return result;
 }
+
+lbool solver::check_sat(unsigned num_assumptions, expr * const * assumptions) {
+    lbool r = l_undef;
+    try {
+        r = check_sat_core(num_assumptions, assumptions);
+    }
+    catch (...) {
+        if (get_manager().canceled()) {
+            dump_state(num_assumptions, assumptions);
+        }
+        throw;
+    }
+    if (r == l_undef && get_manager().canceled()) {
+        dump_state(num_assumptions, assumptions);        
+    }
+    return r;
+}
+
+void solver::dump_state(unsigned sz, expr* const* assumptions) {
+    std::string file = m_cancel_backup_file.str();
+    if (file != "") {
+        std::ofstream ous(file);
+        display(ous, sz, assumptions);
+    }
+}
diff --git a/src/solver/solver.h b/src/solver/solver.h
index 7437a5a08..161677cb5 100644
--- a/src/solver/solver.h
+++ b/src/solver/solver.h
@@ -44,8 +44,9 @@ public:
      - results based on check_sat_result API
 */
 class solver : public check_sat_result {
-    params_ref m_params;
-    bool       m_enforce_model_conversion;
+    params_ref  m_params;
+    bool        m_enforce_model_conversion;
+    symbol      m_cancel_backup_file;
 public:
     solver(): m_enforce_model_conversion(false) {}
     ~solver() override {}
@@ -140,7 +141,8 @@ public:
        
        If it is unsatisfiable, and unsat-core generation is enabled. Then, the unsat-core is a subset of these assumptions.
     */
-    virtual lbool check_sat(unsigned num_assumptions, expr * const * assumptions) = 0;
+
+    lbool check_sat(unsigned num_assumptions, expr * const * assumptions);
 
     lbool check_sat(expr_ref_vector const& asms) { return check_sat(asms.size(), asms.c_ptr()); }
     
@@ -227,6 +229,11 @@ public:
     */
     virtual std::ostream& display(std::ostream & out, unsigned n = 0, expr* const* assumptions = nullptr) const;
 
+    /**
+       \brief Display the content of this solver in DIMACS format
+    */
+    std::ostream& display_dimacs(std::ostream & out) const;
+
     /**
        \brief expose model converter when solver produces partially reduced set of assertions.
      */
@@ -249,14 +256,17 @@ public:
         void disable_pop() { m_nopop = true; }
     };
 
+    virtual lbool check_sat_core(unsigned num_assumptions, expr * const * assumptions) = 0;
  
 protected:
 
     virtual lbool get_consequences_core(expr_ref_vector const& asms, expr_ref_vector const& vars, expr_ref_vector& consequences);
 
+    void dump_state(unsigned sz, expr* const* assumptions);
 
     bool is_literal(ast_manager& m, expr* e);
 
+
 };
 
 typedef ref<solver> solver_ref;
diff --git a/src/solver/solver_na2as.cpp b/src/solver/solver_na2as.cpp
index a3fcd0e0b..6173dfddf 100644
--- a/src/solver/solver_na2as.cpp
+++ b/src/solver/solver_na2as.cpp
@@ -61,10 +61,10 @@ struct append_assumptions {
     }
 };
 
-lbool solver_na2as::check_sat(unsigned num_assumptions, expr * const * assumptions) {
+lbool solver_na2as::check_sat_core(unsigned num_assumptions, expr * const * assumptions) {
     append_assumptions app(m_assumptions, num_assumptions, assumptions);
     TRACE("solver_na2as", display(tout););
-    return check_sat_core(m_assumptions.size(), m_assumptions.c_ptr());
+    return check_sat_core2(m_assumptions.size(), m_assumptions.c_ptr());
 }
 
 lbool solver_na2as::check_sat_cc(const expr_ref_vector &assumptions, vector<expr_ref_vector> const &clauses) {
diff --git a/src/solver/solver_na2as.h b/src/solver/solver_na2as.h
index d1515a206..67ec004cc 100644
--- a/src/solver/solver_na2as.h
+++ b/src/solver/solver_na2as.h
@@ -35,10 +35,9 @@ public:
     ~solver_na2as() override;
 
     void assert_expr_core2(expr * t, expr * a) override;
-    // virtual void assert_expr_core(expr * t) = 0;
 
     // Subclasses of solver_na2as should redefine the following *_core methods instead of these ones.
-    lbool check_sat(unsigned num_assumptions, expr * const * assumptions) override;
+    lbool check_sat_core(unsigned num_assumptions, expr * const * assumptions) override;
     lbool check_sat_cc(const expr_ref_vector &assumptions, vector<expr_ref_vector> const &clauses) override;
     void push() override;
     void pop(unsigned n) override;
@@ -49,7 +48,7 @@ public:
     lbool get_consequences(expr_ref_vector const& asms, expr_ref_vector const& vars, expr_ref_vector& consequences) override;
     lbool find_mutexes(expr_ref_vector const& vars, vector<expr_ref_vector>& mutexes) override;
 protected:
-    virtual lbool check_sat_core(unsigned num_assumptions, expr * const * assumptions) = 0;
+    virtual lbool check_sat_core2(unsigned num_assumptions, expr * const * assumptions) = 0;
     virtual lbool check_sat_cc_core(const expr_ref_vector &assumptions, vector<expr_ref_vector> const &clauses) { NOT_IMPLEMENTED_YET(); }
     virtual void push_core() = 0;
     virtual void pop_core(unsigned n) = 0;
diff --git a/src/solver/solver_params.pyg b/src/solver/solver_params.pyg
new file mode 100644
index 000000000..29690a164
--- /dev/null
+++ b/src/solver/solver_params.pyg
@@ -0,0 +1,8 @@
+
+def_module_params('solver', 
+                  description='solver parameters',
+                  export=True,
+                  params=(('enforce_model_conversion', BOOL, False, "apply model transformation on new assertions"),
+                          ('cancel_backup_file', SYMBOL, '', "file to save partial search state if search is canceled"),
+                          ))
+                
diff --git a/src/solver/solver_pool.cpp b/src/solver/solver_pool.cpp
index 598bb6c02..0495e8a3d 100644
--- a/src/solver/solver_pool.cpp
+++ b/src/solver/solver_pool.cpp
@@ -119,7 +119,7 @@ public:
         }
     }
 
-    lbool check_sat_core(unsigned num_assumptions, expr * const * assumptions) override {
+    lbool check_sat_core2(unsigned num_assumptions, expr * const * assumptions) override {
         SASSERT(!m_pushed || get_scope_level() > 0);
         m_proof.reset();
         scoped_watch _t_(m_pool.m_check_watch);
diff --git a/src/solver/tactic2solver.cpp b/src/solver/tactic2solver.cpp
index 492ddd443..298ed9bc5 100644
--- a/src/solver/tactic2solver.cpp
+++ b/src/solver/tactic2solver.cpp
@@ -62,7 +62,7 @@ public:
 
     void push_core() override;
     void pop_core(unsigned n) override;
-    lbool check_sat_core(unsigned num_assumptions, expr * const * assumptions) override;
+    lbool check_sat_core2(unsigned num_assumptions, expr * const * assumptions) override;
 
     void collect_statistics(statistics & st) const override;
     void get_unsat_core(expr_ref_vector & r) override;
@@ -136,7 +136,7 @@ void tactic2solver::pop_core(unsigned n) {
     m_result = nullptr;
 }
 
-lbool tactic2solver::check_sat_core(unsigned num_assumptions, expr * const * assumptions) {
+lbool tactic2solver::check_sat_core2(unsigned num_assumptions, expr * const * assumptions) {
     if (m_tactic.get() == nullptr)
         return l_false;
     ast_manager & m = m_assertions.m();
diff --git a/src/tactic/fd_solver/bounded_int2bv_solver.cpp b/src/tactic/fd_solver/bounded_int2bv_solver.cpp
index 8791a6282..45d1344ba 100644
--- a/src/tactic/fd_solver/bounded_int2bv_solver.cpp
+++ b/src/tactic/fd_solver/bounded_int2bv_solver.cpp
@@ -137,9 +137,9 @@ public:
         }
     }
 
-    lbool check_sat_core(unsigned num_assumptions, expr * const * assumptions) override {
+    lbool check_sat_core2(unsigned num_assumptions, expr * const * assumptions) override {
         flush_assertions();
-        return m_solver->check_sat(num_assumptions, assumptions);
+        return m_solver->check_sat_core(num_assumptions, assumptions);
     }
 
     void updt_params(params_ref const & p) override { solver::updt_params(p); m_solver->updt_params(p);  }
diff --git a/src/tactic/fd_solver/enum2bv_solver.cpp b/src/tactic/fd_solver/enum2bv_solver.cpp
index 185f23d13..b9a564542 100644
--- a/src/tactic/fd_solver/enum2bv_solver.cpp
+++ b/src/tactic/fd_solver/enum2bv_solver.cpp
@@ -78,9 +78,9 @@ public:
         m_rewriter.pop(n);
     }
 
-    lbool check_sat_core(unsigned num_assumptions, expr * const * assumptions) override {
+    lbool check_sat_core2(unsigned num_assumptions, expr * const * assumptions) override {
         m_solver->updt_params(get_params());
-        return m_solver->check_sat(num_assumptions, assumptions);
+        return m_solver->check_sat_core(num_assumptions, assumptions);
     }
 
     void updt_params(params_ref const & p) override { solver::updt_params(p); m_solver->updt_params(p);  }
diff --git a/src/tactic/fd_solver/pb2bv_solver.cpp b/src/tactic/fd_solver/pb2bv_solver.cpp
index fd4fb8e73..b3620c8ec 100644
--- a/src/tactic/fd_solver/pb2bv_solver.cpp
+++ b/src/tactic/fd_solver/pb2bv_solver.cpp
@@ -75,9 +75,9 @@ public:
         m_rewriter.pop(n);
     }
 
-    lbool check_sat_core(unsigned num_assumptions, expr * const * assumptions) override {
+    lbool check_sat_core2(unsigned num_assumptions, expr * const * assumptions) override {
         flush_assertions();
-        return m_solver->check_sat(num_assumptions, assumptions);
+        return m_solver->check_sat_core(num_assumptions, assumptions);
     }
 
     void updt_params(params_ref const & p) override { solver::updt_params(p); m_rewriter.updt_params(p); m_solver->updt_params(p);  }
diff --git a/src/tactic/goal.cpp b/src/tactic/goal.cpp
index 8f8b86a65..c2d93fa2a 100644
--- a/src/tactic/goal.cpp
+++ b/src/tactic/goal.cpp
@@ -20,6 +20,7 @@ Revision History:
 #include "ast/ast_smt2_pp.h"
 #include "ast/for_each_expr.h"
 #include "ast/well_sorted.h"
+#include "ast/display_dimacs.h"
 #include "tactic/goal.h"
 
 goal::precision goal::mk_union(precision p1, precision p2) {
@@ -262,14 +263,14 @@ void goal::assert_expr(expr * f, expr_dependency * d) {
     assert_expr(f, proofs_enabled() ? m().mk_asserted(f) : nullptr, d);
 }
 
-void goal::get_formulas(ptr_vector<expr> & result) {
+void goal::get_formulas(ptr_vector<expr> & result) const {
     unsigned sz = size();
     for (unsigned i = 0; i < sz; i++) {
         result.push_back(form(i));
     }
 }
 
-void goal::get_formulas(expr_ref_vector & result) {
+void goal::get_formulas(expr_ref_vector & result) const {
     unsigned sz = size();
     for (unsigned i = 0; i < sz; i++) {
         result.push_back(form(i));
@@ -434,63 +435,9 @@ void goal::display_ll(std::ostream & out) const {
    \brief Assumes that the formula is already in CNF.
 */
 void goal::display_dimacs(std::ostream & out) const {
-    unsigned_vector expr2var;
-    ptr_vector<expr> exprs;
-    unsigned num_vars = 0;
-    unsigned num_cls  = size();
-    for (unsigned i = 0; i < num_cls; i++) {
-        expr * f = form(i);
-        unsigned num_lits;
-        expr * const * lits;
-        if (m().is_or(f)) {
-            num_lits = to_app(f)->get_num_args();
-            lits     = to_app(f)->get_args();
-        }
-        else {
-            num_lits = 1;
-            lits     = &f;
-        }
-        for (unsigned j = 0; j < num_lits; j++) {
-            expr * l = lits[j];
-            if (m().is_not(l))
-                l = to_app(l)->get_arg(0);
-            if (expr2var.get(l->get_id(), UINT_MAX) == UINT_MAX) {
-                num_vars++;
-                expr2var.setx(l->get_id(), num_vars, UINT_MAX);
-                exprs.setx(l->get_id(), l, nullptr);
-            }
-        }
-    }
-    out << "p cnf " << num_vars << " " << num_cls << "\n";
-    for (unsigned i = 0; i < num_cls; i++) {
-        expr * f = form(i);
-        unsigned num_lits;
-        expr * const * lits;
-        if (m().is_or(f)) {
-            num_lits = to_app(f)->get_num_args();
-            lits     = to_app(f)->get_args();
-        }
-        else {
-            num_lits = 1;
-            lits     = &f;
-        }
-        for (unsigned j = 0; j < num_lits; j++) {
-            expr * l = lits[j];
-            if (m().is_not(l)) {
-                out << "-";
-                l = to_app(l)->get_arg(0);
-            }
-            SASSERT(exprs[l->get_id()]);
-            out << expr2var[l->get_id()] << " ";
-        }
-        out << "0\n";
-    }
-    for (expr* e : exprs) {
-        if (e && is_app(e)) {
-            symbol const& n = to_app(e)->get_decl()->get_name();
-            out << "c " << expr2var[e->get_id()] << " " << n << "\n";            
-        }
-    }
+    expr_ref_vector fmls(m());
+    get_formulas(fmls);
+    ::display_dimacs(out, fmls);
 }
 
 unsigned goal::num_exprs() const {
diff --git a/src/tactic/goal.h b/src/tactic/goal.h
index fa2f16eb6..33f9298ab 100644
--- a/src/tactic/goal.h
+++ b/src/tactic/goal.h
@@ -126,8 +126,8 @@ public:
 
     void update(unsigned i, expr * f, proof * pr = nullptr, expr_dependency * dep = nullptr);
 
-    void get_formulas(ptr_vector<expr> & result);
-    void get_formulas(expr_ref_vector & result);
+    void get_formulas(ptr_vector<expr> & result) const;
+    void get_formulas(expr_ref_vector & result) const;
     
     void elim_true();
     void elim_redundancies();
diff --git a/src/util/chashtable.h b/src/util/chashtable.h
index e49ac3bd4..19ff1ef51 100644
--- a/src/util/chashtable.h
+++ b/src/util/chashtable.h
@@ -32,6 +32,7 @@ Revision History:
 #include "util/debug.h"
 #include "util/trace.h"
 #include "util/tptr.h"
+#include "util/util.h"
 #ifdef Z3DEBUG
 #include "util/hashtable.h"
 #endif