diff --git a/src/opt/weighted_maxsat.cpp b/src/opt/weighted_maxsat.cpp
index d3816bdaf..c1b22f075 100644
--- a/src/opt/weighted_maxsat.cpp
+++ b/src/opt/weighted_maxsat.cpp
@@ -37,6 +37,7 @@ Notes:
 #include "opt_sls_solver.h"
 #include "cancel_eh.h"
 #include "scoped_timer.h"
+#include "optsmt.h"
 
 namespace opt {
 
@@ -611,7 +612,11 @@ namespace opt {
         };
 
         scoped_ptr<maxsmt_solver_base> maxs;
+        optsmt                  m_optsmt;     // hitting set optimizer based on simplex.
+        opt_solver              m_solver;
+        unsigned                m_objective;  // index of objective
         expr_ref_vector         m_aux;        // auxiliary (indicator) variables.
+        expr_ref_vector         m_iaux;       // auxiliary integer (indicator) variables.
         expr_ref_vector         m_naux;       // negation of auxiliary variables.
         obj_map<expr, unsigned> m_aux2index;  // expr |-> index
         unsigned_vector         m_core_activity; // number of times soft constraint is used in a core.
@@ -619,6 +624,7 @@ namespace opt {
         svector<bool>           m_aux_active; // active soft clauses.
         ptr_vector<expr>        m_asms;       // assumptions (over aux)
         pb_util                 pb;
+        arith_util              a;
         stats                   m_stats;
 
 
@@ -626,20 +632,30 @@ namespace opt {
         hsmax(solver* s, ast_manager& m, maxsmt_solver_base* maxs):
             maxsmt_solver_base(s, m), 
             maxs(maxs), 
+            m_optsmt(m),
+            m_solver(m, m_params, symbol()),
             m_aux(m), 
+            m_iaux(m),
             m_naux(m),
-            pb(m) {
+            pb(m),
+            a(m) {
         }
         virtual ~hsmax() {}
 
         virtual void set_cancel(bool f) { 
             maxsmt_solver_base::set_cancel(f); 
-            maxs->set_cancel(f); 
+            // maxs->set_cancel(f);
+            m_optsmt.set_cancel(f);
+        }
+
+        virtual void updt_params(params_ref& p) {
+            maxsmt_solver_base::updt_params(p);
+            m_solver.updt_params(p);
         }
 
         virtual void collect_statistics(statistics& st) const {
             maxsmt_solver_base::collect_statistics(st);
-            maxs->collect_statistics(st);
+            // maxs->s().collect_statistics(st);
             st.update("hsmax-num-iterations", m_stats.m_num_iterations);
             st.update("hsmax-num-core-reductions-n", m_stats.m_num_core_reductions_failure);
             st.update("hsmax-num-core-reductions-y", m_stats.m_num_core_reductions_success);
@@ -702,9 +718,12 @@ namespace opt {
 
         void init_local() {
             unsigned sz = num_soft();
+            app_ref  fml(m), obj(m);
+            expr_ref_vector sum(m);
             m_asms.reset();
             m_seed.reset();           
             m_aux.reset();
+            m_iaux.reset();
             m_naux.reset();
             m_aux_active.reset();            
             m_aux2index.reset();
@@ -712,17 +731,28 @@ namespace opt {
             for (unsigned i = 0; i < sz; ++i) {
                 bool tt = is_true(m_model, m_soft[i].get());
                 m_seed.push_back(tt);
-                m_aux. push_back(mk_fresh());
+                m_aux. push_back(mk_fresh(m.mk_bool_sort()));
+                m_iaux.push_back(mk_fresh(a.mk_int()));
+                expr* iaux = m_iaux.back();
                 m_naux.push_back(m.mk_not(m_aux.back()));
                 m_aux_active.push_back(false);
                 m_core_activity.push_back(0);
-                m_aux2index.insert(m_aux[i].get(), i);
+                m_aux2index.insert(m_aux.back(), i);
+                m_aux2index.insert(m_iaux.back(), i);
+                fml = m.mk_and(a.mk_le(a.mk_numeral(rational::zero(), true), iaux), 
+                               a.mk_le(iaux, a.mk_numeral(rational::one(), true)));
+                rational const& w = m_weights[i];
+                sum.push_back(a.mk_mul(a.mk_numeral(w, w.is_int()), iaux));
+                m_solver.assert_expr(fml);
                 if (tt) {
                     m_asms.push_back(m_aux.back());
                     ensure_active(i);
                 }
             }
-            maxs->init_soft(m_weights, m_aux);
+            obj = a.mk_add(sum.size(), sum.c_ptr());
+            m_objective = m_optsmt.add(obj);
+            m_optsmt.setup(m_solver);
+            // maxs->init_soft(m_weights, m_aux);
             TRACE("opt", print_seed(tout););
         }
 
@@ -858,18 +888,6 @@ namespace opt {
             }
         }
 
-        struct cancel_maxs {
-            hsmax& hs;
-            cancel_maxs(hsmax& hs):hs(hs) {}
-            void reset_cancel() {
-                hs.maxs->set_cancel(false);
-            }
-            void cancel() {
-                hs.maxs->set_cancel(true);
-            }
-        };
-
-
         //
         // retrieve the next seed that satisfies state of maxs.
         // state of maxs must be satisfiable before optimization is called.
@@ -881,6 +899,26 @@ namespace opt {
         lbool next_seed() {
             scoped_stopwatch _sw(m_stats.m_aux_sat_time);
             TRACE("opt", tout << "\n";);
+#if 1
+            m_solver.display(std::cout);
+            lbool is_sat = m_optsmt.lex(m_objective);
+            if (is_sat == l_true) {
+                model_ref mdl;
+                m_optsmt.get_model(mdl);
+                
+                for (unsigned i = 0; i < num_soft(); ++i) {
+                    if (is_active(i)) {
+                        m_seed[i] = is_one(mdl, m_iaux[i].get());
+                    }
+                    else {
+                        m_seed[i] = false;
+                    }
+                }
+                print_seed(std::cout);
+                TRACE("opt", print_seed(tout););
+            }
+            
+#else
             lbool is_sat = maxs->s().check_sat(0,0);
             if (is_sat == l_true) {
                 maxs->set_model();
@@ -903,6 +941,7 @@ namespace opt {
                 }
                 TRACE("opt", print_seed(tout););
             }
+#endif
             return is_sat;
         }
 
@@ -1070,6 +1109,16 @@ namespace opt {
             }
             expr_ref_vector fmls(m);
             expr_ref fml(m);
+#if 1
+            for (unsigned i = 0; i < num_soft(); ++i) {
+                if (!indices.contains(i)) {
+                    fmls.push_back(m_iaux[i].get());
+                }
+            }
+            fml = a.mk_ge(a.mk_add(fmls.size(), fmls.c_ptr()), a.mk_numeral(rational::one(), true));
+            m_solver.assert_expr(fml);
+
+#else
             for (unsigned i = 0; i < num_soft(); ++i) {
                 if (!indices.contains(i)) {
                     fmls.push_back(m_aux[i].get());
@@ -1077,8 +1126,9 @@ namespace opt {
             }
             fml = m.mk_or(fmls.size(), fmls.c_ptr());
             maxs->add_hard(fml);
+#endif
             TRACE("opt", tout << fml << "\n";);
-            set_upper();
+            // set_upper();
         }
 
         // constrain the upper bound.
@@ -1093,13 +1143,25 @@ namespace opt {
         void block_up() {
             expr_ref_vector fmls(m);
             expr_ref fml(m);
+#if 1
             for (unsigned i = 0; i < m_asms.size(); ++i) {
+                unsigned index = m_aux2index.find(m_asms[i]);
+                m_core_activity[index]++;
+                fmls.push_back(m_iaux[index].get());
+            }
+            fml = a.mk_lt(a.mk_add(fmls.size(), fmls.c_ptr()), a.mk_numeral(rational(fmls.size()), true));
+            TRACE("opt", tout << fml << "\n";);
+            m_solver.assert_expr(fml);
+#else
+            for (unsigned i = 0; i < m_asms.size(); ++i) {
+                unsigned index = m_aux2index.find(m_asms[i]);
                 fmls.push_back(m.mk_not(m_asms[i]));
-                m_core_activity[m_aux2index.find(m_asms[i])]++;
+                m_core_activity[index]++;
             }
             fml = m.mk_or(fmls.size(), fmls.c_ptr());
             TRACE("opt", tout << fml << "\n";);
             maxs->add_hard(fml);            
+#endif
         }
 
 
@@ -1113,19 +1175,28 @@ namespace opt {
             }
         }        
 
-        app_ref mk_fresh() {
+        app_ref mk_fresh(sort* s) {
             app_ref r(m);
-            r = m.mk_fresh_const("r", m.mk_bool_sort());
+            r = m.mk_fresh_const("r", s);
             m_mc->insert(r->get_decl());                
             return r;
         }
 
+
         bool is_true(model_ref& mdl, expr* e) {
             expr_ref val(m);
             VERIFY(mdl->eval(e, val));
             return m.is_true(val);
         }
 
+        bool is_one(model_ref& mdl, expr* e) {
+            rational r;
+            expr_ref val(m);
+            VERIFY(mdl->eval(e, val));
+            std::cout << mk_pp(e, m) << " |-> " << val << "\n";
+            return a.is_numeral(val, r) && r.is_one();
+        }
+
         bool is_active(unsigned i) const {
             return m_aux_active[i];
         }
diff --git a/src/smt/theory_arith.h b/src/smt/theory_arith.h
index 2e8c62393..0ddaf67d9 100644
--- a/src/smt/theory_arith.h
+++ b/src/smt/theory_arith.h
@@ -857,7 +857,7 @@ namespace smt {
         void add_tmp_row(row & r1, numeral const & coeff, row const & r2);
         theory_var pick_var_to_leave(bool has_int, theory_var x_j, bool inc, numeral & a_ij, inf_numeral & gain, bool& skiped_row);
         bool is_safe_to_leave(theory_var x, bool& has_int);
-        void move_to_bound(theory_var x_i, bool inc);
+        bool move_to_bound(theory_var x_i, bool inc);
         template<bool invert>
         void add_tmp_row_entry(row & r, numeral const & coeff, theory_var v);
         enum max_min_t { UNBOUNDED, AT_BOUND, OPTIMIZED, BEST_EFFORT};
@@ -1061,6 +1061,7 @@ namespace smt {
         bool valid_row_assignment() const;
         bool valid_row_assignment(row const & r) const;
         bool satisfy_bounds() const;
+        bool satisfy_integrality() const;
 #endif
     };
     
diff --git a/src/smt/theory_arith_aux.h b/src/smt/theory_arith_aux.h
index 7a84b3a8b..1e2a6c238 100644
--- a/src/smt/theory_arith_aux.h
+++ b/src/smt/theory_arith_aux.h
@@ -1069,7 +1069,7 @@ namespace smt {
 
     template<typename Ext>
     inf_eps_rational<inf_rational> theory_arith<Ext>::maximize(theory_var v, expr_ref& blocker) {
-        TRACE("opt", tout << "data-size: " << m_data.size() << "\n";);
+        TRACE("bound_bug", display_var(tout, v); display(tout););
         max_min_t r = max_min(v, true); 
         if (r == UNBOUNDED) {
             blocker = get_manager().mk_false();
@@ -1361,7 +1361,8 @@ namespace smt {
                 }
             }
             TRACE("opt", tout << "after traversing row:\nx_i: v" << x_i << ", x_j: v" << x_j << ", gain: " << gain << "\n";
-                  tout << "skipped row: " << (skipped_row?"yes":"no") << "\n";);
+                  tout << "skipped row: " << (skipped_row?"yes":"no") << "\n";
+                  display(tout););
 
             if (x_j == null_theory_var) {
                 TRACE("opt", tout << "row is " << (max ? "maximized" : "minimized") << "\n";);
@@ -1378,6 +1379,7 @@ namespace smt {
                     TRACE("opt", tout << "moved v" << x_j << " to upper bound\n";);
                     SASSERT(valid_row_assignment());
                     SASSERT(satisfy_bounds());
+                    SASSERT(satisfy_integrality());
                     continue;
                 }
                 if (!inc && lower(x_j)) {
@@ -1385,13 +1387,14 @@ namespace smt {
                     TRACE("opt", tout << "moved v" << x_j << " to lower bound\n";);
                     SASSERT(valid_row_assignment());
                     SASSERT(satisfy_bounds());
+                    SASSERT(satisfy_integrality());
                     continue;
                 }
                 result = skipped_row?BEST_EFFORT:UNBOUNDED;
                 break;
             }
 
-            if (!is_fixed(x_j) && is_bounded(x_j) && (upper_bound(x_j) - lower_bound(x_j) <= gain)) {
+            if (!is_fixed(x_j) && is_bounded(x_j) && !skipped_row && (upper_bound(x_j) - lower_bound(x_j) <= gain)) {
                 // can increase/decrease x_j up to upper/lower bound.
                 if (inc) {
                     update_value(x_j, upper_bound(x_j) - get_value(x_j));
@@ -1403,6 +1406,7 @@ namespace smt {
                 }
                 SASSERT(valid_row_assignment());
                 SASSERT(satisfy_bounds());
+                SASSERT(satisfy_integrality());
                 continue;
             }
 
@@ -1425,7 +1429,10 @@ namespace smt {
                 move_xi_to_lower = a_ij.is_pos();
             else
                 move_xi_to_lower = a_ij.is_neg();
-            move_to_bound(x_i, move_xi_to_lower);
+            if (!move_to_bound(x_i, move_xi_to_lower)) {
+                result = BEST_EFFORT;
+                break;
+            }
 
             row & r2 = m_rows[get_var_row(x_j)];
             coeff.neg();
@@ -1433,6 +1440,7 @@ namespace smt {
             SASSERT(r.get_idx_of(x_j) == -1);
             SASSERT(valid_row_assignment());
             SASSERT(satisfy_bounds());
+            SASSERT(satisfy_integrality());
         }
         TRACE("opt", display(tout););
         return result;
@@ -1444,7 +1452,7 @@ namespace smt {
     */
 
     template<typename Ext>
-    void theory_arith<Ext>::move_to_bound(theory_var x_i, bool move_to_lower) {
+    bool theory_arith<Ext>::move_to_bound(theory_var x_i, bool move_to_lower) {
         inf_numeral delta, delta_abs;
 
         if (move_to_lower) {
@@ -1484,6 +1492,9 @@ namespace smt {
             }
         }
 
+        if (is_int(x_i)) {
+            delta_abs = floor(delta_abs);
+        }
 
         if (move_to_lower) {
             delta = -delta_abs;
@@ -1493,8 +1504,8 @@ namespace smt {
         }
 
         TRACE("opt", tout << "Safe delta: " << delta << "\n";);
-
         update_value(x_i, delta);
+        return !delta.is_zero();
     }
 
     /**
diff --git a/src/smt/theory_arith_inv.h b/src/smt/theory_arith_inv.h
index 80bb9307f..f6270e664 100644
--- a/src/smt/theory_arith_inv.h
+++ b/src/smt/theory_arith_inv.h
@@ -199,6 +199,18 @@ namespace smt {
         }
         return true;
     }
+
+    template<typename Ext>
+    bool theory_arith<Ext>::satisfy_integrality() const {
+        int num = get_num_vars();
+        for (theory_var v = 0; v < num; v++) {
+            if (!(is_int(v) && get_value(v).is_int())) {
+                TRACE("bound_bug", display_var(tout, v); display(tout););
+                return false;
+            }
+        }
+        return true;
+    }
 #endif
 
 };