diff --git a/src/opt/mus.cpp b/src/opt/mus.cpp
index f9190911a..7f265ab0f 100644
--- a/src/opt/mus.cpp
+++ b/src/opt/mus.cpp
@@ -78,7 +78,7 @@ struct mus::imp {
         expr_ref_vector assumptions(m);
         ptr_vector<expr> core_exprs;
         while (!core.empty()) { 
-            IF_VERBOSE(1, verbose_stream() << "(opt.mus reducing core: " << core.size() << " new core: " << mus.size() << ")\n";);
+            IF_VERBOSE(2, verbose_stream() << "(opt.mus reducing core: " << core.size() << " new core: " << mus.size() << ")\n";);
             unsigned cls_id = core.back();
             TRACE("opt", 
                   display_vec(tout << "core:  ", core);
diff --git a/src/smt/theory_arith_core.h b/src/smt/theory_arith_core.h
index 264eb0f10..3ac70d372 100644
--- a/src/smt/theory_arith_core.h
+++ b/src/smt/theory_arith_core.h
@@ -72,6 +72,7 @@ namespace smt {
             m_value        .push_back(inf_numeral());
         }
         m_old_value        .push_back(inf_numeral());
+        SASSERT(m_var_occs.size() == r);
         m_var_occs         .push_back(atoms());
         m_unassigned_atoms .push_back(0);
         m_var_pos          .push_back(-1);
@@ -85,6 +86,7 @@ namespace smt {
         if (is_pure_monomial(n->get_owner()))
             m_nl_monomials.push_back(r);
         SASSERT(check_vector_sizes());
+        SASSERT(m_var_occs[r].empty());
         TRACE("mk_arith_var", 
               tout << "#" << n->get_owner_id() << " :=\n" << mk_ll_pp(n->get_owner(), get_manager()) << "\n";
               tout << "is_attached_to_var: " << is_attached_to_var(n) << ", var: " << n->get_th_var(get_id()) << "\n";);
@@ -812,6 +814,7 @@ namespace smt {
     void theory_arith<Ext>::mk_bound_axioms(atom * a1) {
         theory_var v = a1->get_var();
         atoms & occs = m_var_occs[v];
+        TRACE("mk_bound_axioms", tout << "add bound axioms for v" << v << " " << a1 << "\n";);
         if (!get_context().is_searching()) {
             //
             // NB. We make an assumption that user push calls propagation 
@@ -823,7 +826,7 @@ namespace smt {
         }
         inf_numeral const & k1(a1->get_k());
         atom_kind kind1 = a1->get_atom_kind();
-        TRACE("mk_bound_axioms", tout << "making bound axioms for v" << v << " " << kind1 << " " << k1 << "\n";);
+        TRACE("mk_bound_axioms", tout << "making bound axioms for v" << v << " " << kind1 << " " << k1 << " " << a1 << "\n";);
         typename atoms::iterator it  = occs.begin();
         typename atoms::iterator end = occs.end();
 
@@ -833,6 +836,12 @@ namespace smt {
             atom * a2 = *it;            
             inf_numeral const & k2(a2->get_k());
             atom_kind kind2 = a2->get_atom_kind();
+            CTRACE("mk_bound_axioms", k1 == k2 && kind1 == kind2, 
+                   display_atom(tout << a1 << " ", a1, true);
+                   display_atom(tout << a2 << " ", a2, true);
+                   tout << &occs << " " << &m_var_occs[v] << "\n";
+                   );
+
             SASSERT(k1 != k2 || kind1 != kind2);
             if (kind2 == A_LOWER) {
                 if (k2 < k1) {
@@ -861,6 +870,7 @@ namespace smt {
 
     template<typename Ext>
     void theory_arith<Ext>::mk_bound_axiom(atom* a1, atom* a2) {
+        TRACE("mk_bound_axioms", tout << a1 << " " << a2 << "\n";);
         theory_var v = a1->get_var();
         literal   l1(a1->get_bool_var()); 
         literal   l2(a2->get_bool_var()); 
@@ -1090,7 +1100,8 @@ namespace smt {
         occs.push_back(a);
         m_atoms.push_back(a);
         insert_bv2a(bv, a);
-        TRACE("arith_internalize", tout << "succeeded... v: " << v << " " << kind << " " << k << "\n";);
+        TRACE("arith_internalize", tout << "succeeded... v" << v << " " << kind << " " << k << "\n";
+              for (unsigned i = 0; i + 1 < occs.size(); ++i) tout << occs[i] << "\n";);
         return true;
     }
 
@@ -2062,7 +2073,7 @@ namespace smt {
                 continue;
             SASSERT(curr_error > inf_numeral(0));
             if (best == null_theory_var || (!least && curr_error > best_error) || (least && curr_error < best_error)) {
-                TRACE("select_pivot", tout << "best: " << best << " v: " << v 
+                TRACE("select_pivot", tout << "best: " << best << " v" << v 
                       << ", best_error: " << best_error << ", curr_error: " << curr_error << "\n";);
                 best = v;
                 best_error = curr_error;
@@ -2619,9 +2630,9 @@ namespace smt {
                       << limit_k1 << " delta: " << delta << " coeff: " << coeff << "\n";);
                 inf_numeral k_2 = k_1;
                 atom * new_atom = 0;
-                atoms & as           = m_var_occs[it->m_var];
-                typename atoms::iterator it  = as.begin();
-                typename atoms::iterator end = as.end();
+                atoms const & as           = m_var_occs[it->m_var];
+                typename atoms::const_iterator it  = as.begin();
+                typename atoms::const_iterator end = as.end();
                 for (; it != end; ++it) {
                     atom * a    = *it;
                     if (a == b)
@@ -3200,6 +3211,7 @@ namespace smt {
             erase_bv2a(bv);
             SASSERT(m_var_occs[v].back() == a);
             m_var_occs[v].pop_back();
+            TRACE("mk_bound_axioms", tout << a << "\n";);
             dealloc(a);
         }    
         m_atoms.shrink(old_size);
@@ -3269,6 +3281,7 @@ namespace smt {
             m_bounds[1]       .shrink(old_num_vars);
             SASSERT(check_vector_sizes());
         }
+        SASSERT(m_var_occs.size() == old_num_vars);
     }
 
     template<typename Ext>