diff --git a/src/math/lp/nla_expr.h b/src/math/lp/nla_expr.h
index bdb7a5d07..31bc579af 100644
--- a/src/math/lp/nla_expr.h
+++ b/src/math/lp/nla_expr.h
@@ -67,6 +67,8 @@ class nla_expr {
         nla_expr& back() { return m_es.back(); }
         const nla_expr* begin() const { return m_es.begin(); }
         const nla_expr* end() const { return m_es.end(); }
+        typename std::vector<nla_expr>::iterator begin() { return m_es.begin(); }
+        typename std::vector<nla_expr>::iterator end() { return m_es.end(); }
         unsigned size() const { return m_es.size(); }
         void sort() {
             std::sort(m_order.begin(), m_order.end(), [this](unsigned i, unsigned j) { return m_es[i] < m_es[j]; });
@@ -127,13 +129,12 @@ public:
     }
 
     void simplify() {
+        if (is_simple()) return;
+        bool has_sum = false;
         if (is_sum()) {
-            bool has_sum = false;
-            for (unsigned j = 0; j < m_children.es().size(); j++) {
-                auto& e = m_children.es()[j];
+            for (auto & e : m_children) {
                 e.simplify();
-                if (e.is_sum())
-                    has_sum = true;
+                has_sum |= e.is_sum();
             }
             if (has_sum) {
                 nla_expr n(expr_type::SUM);
@@ -141,15 +142,12 @@ public:
                     n += e;
                 }
                 *this = n;
-            }
-            
+            }        
         } else if (is_mul()) {
             bool has_mul = false;
-            for (unsigned j = 0; j < m_children.es().size(); j++) {
-                auto& e = m_children.es()[j];
+            for (auto & e : m_children) {
                 e.simplify();
-                if (e.is_mul())
-                    has_mul = true;
+                has_mul |= e.is_mul();
             }
             if (has_mul) {
                 nla_expr n(expr_type::MUL);
@@ -209,7 +207,7 @@ public:
         switch(m_type) {
         case expr_type::SUM:
         case expr_type::MUL:
-            return m_children.size() <= 1;
+            return false;
         
         default:
             return true;