diff --git a/src/ast/ast.cpp b/src/ast/ast.cpp
index 2fe59d608..712e892c4 100644
--- a/src/ast/ast.cpp
+++ b/src/ast/ast.cpp
@@ -1911,7 +1911,7 @@ void ast_manager::delete_node(ast * n) {
     while ((n = m_ast_table.pop_erase())) {
 
         CTRACE("del_quantifier", is_quantifier(n), tout << "deleting quantifier " << n->m_id << " " << n << "\n";);
-        TRACE("mk_var_bug", tout << "del_ast: " << n->m_id << "\n";);
+        TRACE("mk_var_bug", tout << "del_ast: " << " " << n->m_ref_count << "\n";);
         TRACE("ast_delete_node", tout << mk_bounded_pp(n, *this) << "\n";);
 
         SASSERT(!m_debug_ref_count || !m_debug_free_indices.contains(n->m_id));
diff --git a/src/math/grobner/grobner.cpp b/src/math/grobner/grobner.cpp
index f26a9a550..329c08f92 100644
--- a/src/math/grobner/grobner.cpp
+++ b/src/math/grobner/grobner.cpp
@@ -65,19 +65,14 @@ void grobner::del_equation(equation * eq) {
 }
 
 void grobner::del_monomials(ptr_vector<monomial>& ms) {
-    ptr_vector<monomial>::iterator it  = ms.begin();
-    ptr_vector<monomial>::iterator end = ms.end();
-    for (; it != end; ++it) {
-        del_monomial(*it);
+    for (auto& m : ms) {
+        del_monomial(m);
     }
     ms.reset();
 }
 
 void grobner::del_monomial(monomial * m) {
-    ptr_vector<expr>::iterator it2  = m->m_vars.begin();
-    ptr_vector<expr>::iterator end2 = m->m_vars.end();
-    for (; it2 != end2; ++it2) {
-        expr * v = *it2;
+    for (expr * v : m->m_vars) {
         m_manager.dec_ref(v);
     }
     dealloc(m);
@@ -187,10 +182,8 @@ void grobner::display_equation(std::ostream & out, equation const & eq) const {
 void grobner::display_equations(std::ostream & out, equation_set const & v, char const * header) const {
     if (!v.empty()) {
         out << header << "\n";
-        equation_set::iterator it  = v.begin();
-        equation_set::iterator end = v.end();
-        for (; it != end; ++it)
-            display_equation(out, *(*it));
+        for (equation const* eq : v) 
+            display_equation(out, *eq);
     }
 }
 
@@ -215,10 +208,7 @@ bool grobner::update_order(equation * eq) {
     if (eq->get_num_monomials() == 0)
         return false;
     monomial * first = eq->m_monomials[0];
-    ptr_vector<monomial>::iterator it  = eq->m_monomials.begin();
-    ptr_vector<monomial>::iterator end = eq->m_monomials.end();
-    for (; it != end; ++it) {
-        monomial * m = *it;
+    for (monomial* m : eq->m_monomials) {
         std::stable_sort(m->m_vars.begin(), m->m_vars.end(), m_var_lt);
     }
     std::stable_sort(eq->m_monomials.begin(), eq->m_monomials.end(), m_monomial_lt);
@@ -227,10 +217,7 @@ bool grobner::update_order(equation * eq) {
 
 void grobner::update_order(equation_set & s, bool processed) {
     ptr_buffer<equation> to_remove;
-    equation_set::iterator it  = s.begin();
-    equation_set::iterator end = s.end();
-    for (;it != end; ++it) {
-        equation * eq = *it;
+    for (equation * eq : s) {
         if (update_order(eq)) {
             if (processed) {
                 to_remove.push_back(eq);
@@ -238,10 +225,8 @@ void grobner::update_order(equation_set & s, bool processed) {
             }
         }
     }
-    ptr_buffer<equation>::iterator it2  = to_remove.begin();
-    ptr_buffer<equation>::iterator end2 = to_remove.end();
-    for (; it2 != end2; ++it2)
-        s.erase(*it2);
+    for (equation* e : to_remove) 
+        s.erase(e);
 }
 
 void grobner::update_order() {
@@ -582,10 +567,8 @@ void grobner::mul_append(unsigned start_idx, equation const * source, rational c
         new_m->m_coeff    *= coeff;
         new_m->m_vars.append(m->m_vars.size(), m->m_vars.c_ptr());
         new_m->m_vars.append(vars.size(), vars.c_ptr());
-        ptr_vector<expr>::iterator it  = new_m->m_vars.begin();
-        ptr_vector<expr>::iterator end = new_m->m_vars.end();
-        for (; it != end; ++it)
-            m_manager.inc_ref(*it);
+        for (expr* e : new_m->m_vars) 
+            m_manager.inc_ref(e);
         std::stable_sort(new_m->m_vars.begin(), new_m->m_vars.end(), m_var_lt);
         result.push_back(new_m);
     }
@@ -597,10 +580,8 @@ void grobner::mul_append(unsigned start_idx, equation const * source, rational c
 grobner::monomial * grobner::copy_monomial(monomial const * m) {
     monomial * r = alloc(monomial);
     r->m_coeff   = m->m_coeff;
-    ptr_vector<expr>::const_iterator it  = m->m_vars.begin();
-    ptr_vector<expr>::const_iterator end = m->m_vars.end();
-    for (; it != end; ++it) 
-        add_var(r, *it);
+    for (expr* e : m->m_vars) 
+        add_var(r, e);
     return r;
 }
 
@@ -692,10 +673,7 @@ grobner::equation * grobner::simplify_using_processed(equation * eq) {
     TRACE("grobner", tout << "simplifying: "; display_equation(tout, *eq); tout << "using already processed equalities\n";);
     do {
         simplified = false;
-        equation_set::iterator it  = m_processed.begin();
-        equation_set::iterator end = m_processed.end();
-        for (; it != end; ++it) {
-            equation const * p = *it;
+        for (equation const* p : m_processed) {
             equation * new_eq  = simplify(p, eq);
             if (new_eq) {
                 result     = true;
@@ -735,19 +713,14 @@ bool grobner::is_better_choice(equation * eq1, equation * eq2) {
 grobner::equation * grobner::pick_next() {
     equation * r = nullptr;
     ptr_buffer<equation> to_delete;
-    equation_set::iterator it  = m_to_process.begin();
-    equation_set::iterator end = m_to_process.end();
-    for (; it != end; ++it) {
-        equation * curr     = *it;
+    for (equation * curr : m_to_process) {
         if (is_trivial(curr))
             to_delete.push_back(curr);
         else if (is_better_choice(curr, r))
             r = curr;
     }
-    ptr_buffer<equation>::const_iterator it1  = to_delete.begin();
-    ptr_buffer<equation>::const_iterator end1 = to_delete.end();
-    for (; it1 != end1; ++it1)
-        del_equation(*it1);
+    for (equation * e : to_delete) 
+        del_equation(e);
     if (r)
         m_to_process.erase(r);
     TRACE("grobner", tout << "selected equation: "; if (!r) tout << "<null>\n"; else display_equation(tout, *r););
@@ -791,18 +764,12 @@ bool grobner::simplify_processed(equation * eq) {
         if (is_trivial(curr))
             to_delete.push_back(curr);
     }
-    ptr_buffer<equation>::const_iterator it1  = to_insert.begin();
-    ptr_buffer<equation>::const_iterator end1 = to_insert.end();
-    for (; it1 != end1; ++it1)
-        m_processed.insert(*it1);
-    it1  = to_remove.begin();
-    end1 = to_remove.end();
-    for (; it1 != end1; ++it1)
-        m_processed.erase(*it1);
-    it1  = to_delete.begin();
-    end1 = to_delete.end();
-    for (; it1 != end1; ++it1)
-        del_equation(*it1);
+    for (equation* eq : to_insert) 
+        m_processed.insert(eq);
+    for (equation* eq : to_remove)
+        m_processed.erase(eq);
+    for (equation* eq : to_delete) 
+        del_equation(eq);
     return !m_manager.canceled();
 }
 
@@ -810,13 +777,10 @@ bool grobner::simplify_processed(equation * eq) {
    \brief Use the given equation to simplify to-process terms.
 */
 void grobner::simplify_to_process(equation * eq) {
-    equation_set::iterator it  = m_to_process.begin();
-    equation_set::iterator end = m_to_process.end();
     ptr_buffer<equation> to_insert;
     ptr_buffer<equation> to_remove;
     ptr_buffer<equation> to_delete;
-    for (; it != end; ++it) {
-        equation * curr     = *it;
+    for (equation* curr : m_to_process) {
         equation * new_curr = simplify(eq, curr);
         if (new_curr != nullptr && new_curr != curr) {
             m_equations_to_unfreeze.push_back(curr);
@@ -827,18 +791,12 @@ void grobner::simplify_to_process(equation * eq) {
         if (is_trivial(curr))
             to_delete.push_back(curr);
     }
-    ptr_buffer<equation>::const_iterator it1  = to_insert.begin();
-    ptr_buffer<equation>::const_iterator end1 = to_insert.end();
-    for (; it1 != end1; ++it1)
-        m_to_process.insert(*it1);
-    it1  = to_remove.begin();
-    end1 = to_remove.end();
-    for (; it1 != end1; ++it1)
-        m_to_process.erase(*it1);
-    it1  = to_delete.begin();
-    end1 = to_delete.end();
-    for (; it1 != end1; ++it1)
-        del_equation(*it1);
+    for (equation* eq : to_insert)
+        m_to_process.insert(eq);
+    for (equation* eq : to_remove)
+        m_to_process.erase(eq);
+    for (equation* eq : to_delete)
+        del_equation(eq);
 }
 
 /**
@@ -924,10 +882,7 @@ void grobner::superpose(equation * eq1, equation * eq2) {
    \brief Superpose the given equations with the equations in m_processed.
 */
 void grobner::superpose(equation * eq) {
-    equation_set::iterator it  = m_processed.begin();
-    equation_set::iterator end = m_processed.end();
-    for (; it != end; ++it) {
-        equation * curr        = *it;
+    for (equation * curr : m_processed) {
         superpose(eq, curr);
     }
 }
@@ -971,10 +926,8 @@ bool grobner::compute_basis(unsigned threshold) {
 }
 
 void grobner::copy_to(equation_set const & s, ptr_vector<equation> & result) const {
-    equation_set::iterator it  = s.begin();
-    equation_set::iterator end = s.end();
-    for (; it != end; ++it)
-        result.push_back(*it);
+    for (equation * e : s) 
+        result.push_back(e);
 }
 
 /**
diff --git a/src/model/model.cpp b/src/model/model.cpp
index fe7b9640b..b96fbccdb 100644
--- a/src/model/model.cpp
+++ b/src/model/model.cpp
@@ -313,7 +313,7 @@ void model::cleanup_interp(top_sort& ts, func_decl* f) {
         if (e1 != e2) 
             fi->set_else(e2);
         for (auto& fe : *fi) {
-            expr_ref e2 = cleanup_expr(ts, fe->get_result(), pid);
+            e2 = cleanup_expr(ts, fe->get_result(), pid);
             if (e2 != fe->get_result()) {
                 fi->insert_entry(fe->get_args(), e2);
             }