diff --git a/src/qe/qe.cpp b/src/qe/qe.cpp
index fbdac726c..b6046f1d9 100644
--- a/src/qe/qe.cpp
+++ b/src/qe/qe.cpp
@@ -2500,8 +2500,12 @@ namespace qe {
                     qe_solver_plugin* p = m_plugins[i];
                     solved = p && p->solve(conjs, fml);
                 }                
-                TRACE("qe", tout << (solved?"solved":"not solved") << "\n";
-                            if (solved) tout << mk_ismt2_pp(fml, m) << "\n";);
+                TRACE("qe", 
+                      tout << (solved?"solved":"not solved") << "\n";
+                      if (solved) tout << mk_ismt2_pp(fml, m) << "\n";
+                      tout << *m_vars << "\n";
+                      tout << "contains: " << m_contains.size() << "\n";
+                      );
             }
             while (solved);
         }
@@ -2531,7 +2535,7 @@ namespace qe {
 
         // callback to replace variable at index 'idx' with definition 'def' and updated formula 'fml'
         void elim_var(unsigned idx, expr* fml, expr* def) override {
-            TRACE("qe", tout << mk_pp(m_vars->get(idx), m) << " " << mk_pp(fml, m) << "\n";);
+            TRACE("qe", tout << idx << ": " << mk_pp(m_vars->get(idx), m) << " " << mk_pp(fml, m) << " " << m_contains.size() << "\n";);
             *m_fml = fml;
             m_vars->set(idx, m_vars->get(m_vars->size()-1));
             m_vars->pop_back();
@@ -2544,6 +2548,7 @@ namespace qe {
         void add_var(app* x) override {
             TRACE("qe", tout << "add var: " << mk_pp(x, m) << "\n";);
             m_vars->push_back(x);
+            m_contains.push_back(alloc(contains_app, m, x));
         }
 
         // callback to add constraints in branch.
@@ -2557,9 +2562,8 @@ namespace qe {
 
     private:
         void reset() {
-            for (unsigned i = 0; i < m_contains.size(); ++i) {
-                dealloc (m_contains[i]);
-            }  
+            for (auto* c : m_contains) 
+                dealloc (c);            
             m_contains.reset();
         }
 
@@ -2567,8 +2571,9 @@ namespace qe {
             reset();
             m_fml = &fml;
             m_vars = &vars;
-            for (unsigned i = 0; i < vars.size(); ++i) {
-                m_contains.push_back(alloc(contains_app, m, vars[i].get()));
+            TRACE("qe", tout << "Vars: " << vars << "\n";);
+            for (auto* v  : vars) {
+                m_contains.push_back(alloc(contains_app, m, v));
             }
         }
     };
@@ -2621,9 +2626,9 @@ namespace qe {
             TRACE("qe", tout << "abstracted" << mk_pp(result, m) << "\n";);
             ptr_vector<sort> sorts;
             svector<symbol> names;
-            for (unsigned i = 0; i < vars.size(); ++i) {
-                sorts.push_back(vars[i]->get_decl()->get_range());
-                names.push_back(vars[i]->get_decl()->get_name());
+            for (app* v : vars) {
+                sorts.push_back(v->get_decl()->get_range());
+                names.push_back(v->get_decl()->get_name());
             }
             if (!vars.empty()) {
                 result = m.mk_quantifier(old_q->get_kind(), vars.size(), sorts.c_ptr(), names.c_ptr(), result, 1);
diff --git a/src/qe/qe_arith_plugin.cpp b/src/qe/qe_arith_plugin.cpp
index 14f6c5f0a..cea44043b 100644
--- a/src/qe/qe_arith_plugin.cpp
+++ b/src/qe/qe_arith_plugin.cpp
@@ -735,7 +735,7 @@ namespace qe {
         bool solve(conj_enum& conjs, expr* fml) {
             expr_ref_vector eqs(m);
             extract_equalities(conjs, eqs);
-            return reduce_equations(eqs.size(), eqs.c_ptr(), fml);
+            return reduce_equations(eqs, fml);
         }
 
         // ----------------------------------------------------------------------
@@ -934,9 +934,9 @@ namespace qe {
         // Linear equations eliminate original variables and introduce auxiliary variables.
         // 
         
-        bool reduce_equations(unsigned num_eqs, expr * const* eqs, expr* fml) {
-            for (unsigned i = 0; i < num_eqs; ++i) {
-                if (reduce_equation(eqs[i], fml)) {
+        bool reduce_equations(expr_ref_vector const& eqs, expr* fml) {
+            for (expr* eq : eqs) {
+                if (reduce_equation(eq, fml)) {
                     return true;
                 }
             }
@@ -1077,7 +1077,7 @@ namespace qe {
             m_replace.apply_substitution(x, p1, result);
             simplify(result);            
             m_ctx.elim_var(index-1, result, p1);
-            TRACE("qe", tout << "Reduced: " << mk_pp(result, m) << "\n";);
+            TRACE("qe", tout << "Reduced " << index-1 << " : " << result << "\n";);
             return true;
         }        
 
diff --git a/src/smt/smt_context.cpp b/src/smt/smt_context.cpp
index babb57605..8e4c5d9fb 100644
--- a/src/smt/smt_context.cpp
+++ b/src/smt/smt_context.cpp
@@ -3465,7 +3465,7 @@ namespace smt {
         if (!check_preamble(reset_cancel)) return l_undef;
         SASSERT(at_base_level());
         setup_context(false);
-        if (m_fparams.m_threads > 1) {            
+        if (m_fparams.m_threads > 1 && !m.has_trace_stream()) {            
             expr_ref_vector asms(m, num_assumptions, assumptions);
             parallel p(*this);
             return p(asms);
diff --git a/src/smt/smt_parallel.cpp b/src/smt/smt_parallel.cpp
index f591741a8..31acd8872 100644
--- a/src/smt/smt_parallel.cpp
+++ b/src/smt/smt_parallel.cpp
@@ -62,7 +62,7 @@ namespace smt {
         if (m.has_trace_stream())
             throw default_exception("trace streams have to be off in parallel mode");
 
-
+        
         for (unsigned i = 0; i < num_threads; ++i) {
             smt_params.push_back(ctx.get_fparams());
         }
@@ -183,6 +183,8 @@ namespace smt {
             }
         };
 
+        num_threads = 1;
+
         while (true) {
             vector<std::thread> threads(num_threads);
             for (unsigned i = 0; i < num_threads; ++i) {