diff --git a/src/opt/opt_context.cpp b/src/opt/opt_context.cpp
index 93f7e1acd..69ec91d85 100644
--- a/src/opt/opt_context.cpp
+++ b/src/opt/opt_context.cpp
@@ -37,38 +37,24 @@ namespace opt {
     {
         m_params.set_bool("model", true);
         m_params.set_bool("unsat_core", true);
+        m_solver = alloc(opt_solver, m, m_params, symbol());
     }
 
     void context::optimize() {
 
-        if (!m_solver) {
-            symbol logic;
-            set_solver(alloc(opt_solver, m, m_params, logic));
-        }
-
-        // really just works for opt_solver now.
-        solver* s = m_solver.get(); 
-        opt_solver::scoped_push _sp(*s);
+        opt_solver& s = *m_solver.get(); 
+        opt_solver::scoped_push _sp(s);
 
         for (unsigned i = 0; i < m_hard_constraints.size(); ++i) {
-            s->assert_expr(m_hard_constraints[i].get());
+            s.assert_expr(m_hard_constraints[i].get());
         }
         
-        lbool is_sat;
-
-        is_sat = m_maxsmt(*s);
-
-        expr_ref_vector ans = m_maxsmt.get_assignment();
-        for (unsigned i = 0; i < ans.size(); ++i) {
-            s->assert_expr(ans[i].get());
-        }
-
+        lbool is_sat = m_maxsmt(s);
         if (is_sat == l_true) {           
-            is_sat = m_optsmt(opt_solver::to_opt(*s));
+            is_sat = m_optsmt(s);
         }
     }
         
-
     void context::set_cancel(bool f) {
         if (m_solver) {
             m_solver->set_cancel(f);
@@ -93,6 +79,7 @@ namespace opt {
             m_solver->updt_params(m_params);
         }
         m_optsmt.updt_params(m_params);
+        m_maxsmt.updt_params(m_params);
     }
 
 
diff --git a/src/opt/opt_context.h b/src/opt/opt_context.h
index df2ca8248..22fd5fd7a 100644
--- a/src/opt/opt_context.h
+++ b/src/opt/opt_context.h
@@ -26,7 +26,7 @@ Notes:
 #define _OPT_CONTEXT_H_
 
 #include "ast.h"
-#include "solver.h"
+#include "opt_solver.h"
 #include "optsmt.h"
 #include "maxsmt.h"
 
@@ -37,7 +37,7 @@ namespace opt {
     class context {
         ast_manager&        m;
         expr_ref_vector     m_hard_constraints;
-        ref<solver>         m_solver;
+        ref<opt_solver>     m_solver;
         params_ref          m_params;
         optsmt              m_optsmt;
         maxsmt              m_maxsmt;
@@ -47,7 +47,6 @@ namespace opt {
         void add_soft_constraint(expr* f, rational const& w) { m_maxsmt.add(f, w); }
         void add_objective(app* t, bool is_max) { m_optsmt.add(t, is_max); }
         void add_hard_constraint(expr* f) { m_hard_constraints.push_back(f);  }
-        void set_solver(solver* s) { m_solver = s; }
         void optimize();
         void set_cancel(bool f);
         void reset_cancel() { set_cancel(false); }
@@ -55,12 +54,6 @@ namespace opt {
         void collect_statistics(statistics& stats);
         static void collect_param_descrs(param_descrs & r);
         void updt_params(params_ref& p);
-
-    private:
-        bool is_maxsat_problem() const;
-
-        opt_solver& get_opt_solver(solver& s); 
-
     };
 
 }
diff --git a/src/opt/optsmt.cpp b/src/opt/optsmt.cpp
index 9c7268913..a6dbd30ab 100644
--- a/src/opt/optsmt.cpp
+++ b/src/opt/optsmt.cpp
@@ -132,9 +132,7 @@ namespace opt {
 
     lbool optsmt::update_upper() {
         smt::theory_opt& opt = s->get_optimizer();
-
         SASSERT(typeid(smt::theory_inf_arith) == typeid(opt));
-
         smt::theory_inf_arith& th = dynamic_cast<smt::theory_inf_arith&>(opt); 
 
         expr_ref bound(m);
@@ -246,13 +244,28 @@ namespace opt {
         return is_sat;
     }
 
-    inf_eps  optsmt::get_value(unsigned index) const {
-        if (m_is_max[index]) {
-            return m_lower[index];
-        }
-        else {
-            return -m_lower[index];
-        }
+    inf_eps optsmt::get_value(unsigned i) const {
+        return m_is_max[i]?m_lower[i]:-m_lower[i];
+    }
+
+    inf_eps optsmt::get_lower(unsigned i) const {
+        return m_is_max[i]?m_lower[i]:-m_upper[i];
+    }
+
+    inf_eps optsmt::get_upper(unsigned i) const {
+        return m_is_max[i]?m_upper[i]:-m_lower[i];
+    }
+
+    // force lower_bound(i) <= objective_value(i)    
+    void optsmt::commit_assignment(unsigned i) {
+        smt::theory_var v = m_vars[i];
+
+        // TBD: this should be a method on all optimization solvers.
+        smt::theory_opt& opt = s->get_optimizer();
+        SASSERT(typeid(smt::theory_inf_arith) == typeid(opt));
+        smt::theory_inf_arith& th = dynamic_cast<smt::theory_inf_arith&>(opt); 
+
+        s->assert_expr(th.block_upper_bound(v, get_lower(i)));
     }
 
     void optsmt::display(std::ostream& out) const {
diff --git a/src/opt/optsmt.h b/src/opt/optsmt.h
index 297f924ae..b892ef38f 100644
--- a/src/opt/optsmt.h
+++ b/src/opt/optsmt.h
@@ -44,6 +44,8 @@ namespace opt {
 
         void add(app* t, bool is_max);
 
+        void commit_assignment(unsigned i);
+
         void set_cancel(bool f);
 
         void updt_params(params_ref& p);
@@ -51,7 +53,9 @@ namespace opt {
         void display(std::ostream& out) const;
 
         inf_eps get_value(unsigned index) const;
-
+        inf_eps get_lower(unsigned index) const;
+        inf_eps get_upper(unsigned index) const;
+        
     private:
         
         lbool basic_opt();