diff --git a/src/ast/euf/euf_egraph.cpp b/src/ast/euf/euf_egraph.cpp
index 691c42981e0..4e8e7327f43 100644
--- a/src/ast/euf/euf_egraph.cpp
+++ b/src/ast/euf/euf_egraph.cpp
@@ -129,7 +129,7 @@ namespace euf {
         return n;
     }
 
-    egraph::egraph(ast_manager& m) : m(m), m_table(m), m_tmp_app(2), m_exprs(m) {
+    egraph::egraph(ast_manager& m) : m(m), m_table(m), m_tmp_app(2), m_exprs(m), m_eq_decls(m) {
         m_tmp_eq = enode::mk_tmp(m_region, 2);
     }
 
@@ -592,7 +592,7 @@ namespace euf {
         SASSERT(!n1->get_root()->m_target);
     }
 
-    bool egraph::are_diseq(enode* a, enode* b) const {
+    bool egraph::are_diseq(enode* a, enode* b) {
         enode* ra = a->get_root(), * rb = b->get_root();
         if (ra == rb)
             return false;
@@ -600,12 +600,16 @@ namespace euf {
             return true;
         if (ra->get_sort() != rb->get_sort())
             return true;
-        expr_ref eq(m.mk_eq(a->get_expr(), b->get_expr()), m);
-        m_tmp_eq->m_args[0] = a;
-        m_tmp_eq->m_args[1] = b;
-        m_tmp_eq->m_expr = eq;
-        SASSERT(m_tmp_eq->num_args() == 2);
-        enode* r = m_table.find(m_tmp_eq);
+        if (ra->num_parents() > rb->num_parents())
+            std::swap(ra, rb);
+        if (ra->num_parents() <= 3) {
+            for (enode* p : enode_parents(ra))
+                if (p->is_equality() && p->get_root()->value() == l_false && 
+                    (rb == p->get_arg(0)->get_root() || rb == p->get_arg(1)->get_root())) 
+                    return true;
+            return false;
+        }
+        enode* r = tmp_eq(ra, rb);
         if (r && r->get_root()->value() == l_false)
             return true;
         return false;
@@ -617,6 +621,24 @@ namespace euf {
         return find(m_tmp_app.get_app(), num_args, args);
     }
 
+    enode* egraph::tmp_eq(enode* a, enode* b) {
+        func_decl* f = nullptr;
+        for (unsigned i = m_eq_decls.size(); i-- > 0; ) {
+            auto e = m_eq_decls.get(i);
+            if (e->get_domain(0) == a->get_sort()) {
+                f = e;
+                break;
+            }                
+        }
+        if (!f) {
+            app_ref eq(m.mk_eq(a->get_expr(), b->get_expr()), m);
+            m_eq_decls.push_back(eq->get_decl());
+            f = eq->get_decl();            
+        }
+        enode* args[2] = { a, b };
+        return get_enode_eq_to(f, 2, args);
+    }
+
     /**
        \brief generate an explanation for a congruence.
        Each pair of children under a congruence have the same roots
@@ -714,12 +736,7 @@ namespace euf {
             explain_eq(justifications, b, rb);
             return sat::null_bool_var;
         }
-        expr_ref eq(m.mk_eq(a->get_expr(), b->get_expr()), m);
-        m_tmp_eq->m_args[0] = a;
-        m_tmp_eq->m_args[1] = b;
-        m_tmp_eq->m_expr = eq;
-        SASSERT(m_tmp_eq->num_args() == 2);
-        enode* r = m_table.find(m_tmp_eq);
+        enode* r = tmp_eq(a, b);
         SASSERT(r && r->get_root()->value() == l_false);
         explain_eq(justifications, r, r->get_root());
         return r->get_root()->bool_var();
diff --git a/src/ast/euf/euf_egraph.h b/src/ast/euf/euf_egraph.h
index 5c828678e8a..7c1f9e5666b 100644
--- a/src/ast/euf/euf_egraph.h
+++ b/src/ast/euf/euf_egraph.h
@@ -165,6 +165,7 @@ namespace euf {
         tmp_app                m_tmp_app;
         enode_vector           m_nodes;
         expr_ref_vector        m_exprs;
+        func_decl_ref_vector   m_eq_decls;
         vector<enode_vector>   m_decl2enodes;
         enode_vector           m_empty_enodes;
         unsigned               m_num_scopes = 0;
@@ -263,10 +264,12 @@ namespace euf {
         /**
         * \brief check if two nodes are known to be disequal.
         */
-        bool are_diseq(enode* a, enode* b) const;
+        bool are_diseq(enode* a, enode* b);
 
         enode* get_enode_eq_to(func_decl* f, unsigned num_args, enode* const* args);
 
+        enode* tmp_eq(enode* a, enode* b);
+
         /**
            \brief Maintain and update cursor into propagated consequences.
            The result of get_literal() is a pair (n, is_eq)
diff --git a/src/sat/smt/q_eval.cpp b/src/sat/smt/q_eval.cpp
index 200b05ec944..c506a52f7e2 100644
--- a/src/sat/smt/q_eval.cpp
+++ b/src/sat/smt/q_eval.cpp
@@ -25,7 +25,10 @@ namespace q {
     struct eval::scoped_mark_reset {
         eval& e;
         scoped_mark_reset(eval& e): e(e) {}
-        ~scoped_mark_reset() { e.m_mark.reset(); }
+        ~scoped_mark_reset() { 
+            e.m_mark.reset(); 
+            e.m_diseq_undef = euf::enode_pair(); 
+        }
     };
 
     eval::eval(euf::solver& ctx):
@@ -97,12 +100,18 @@ namespace q {
         if (sn && sn == tn) 
             return l_true;
         
+        if (sn && sn == m_diseq_undef.first && tn == m_diseq_undef.second) 
+            return l_undef;
+
         if (sn && tn && ctx.get_egraph().are_diseq(sn, tn)) {
             evidence.push_back(euf::enode_pair(sn, tn));
             return l_false;
         }
-        if (sn && tn)
+        if (sn && tn) {
+            m_diseq_undef = euf::enode_pair(sn, tn);
             return l_undef;
+        }
+
         if (!sn && !tn) 
             return compare_rec(n, binding, s, t, evidence);
 
@@ -115,7 +124,11 @@ namespace q {
             std::swap(t, s);
         }        
         unsigned sz = evidence.size();
-        for (euf::enode* t1 : euf::enode_class(tn)) {      
+        unsigned count = 0;
+        for (euf::enode* t1 : euf::enode_class(tn)) { 
+            if (!t1->is_cgr())
+                continue;
+            ++count;
             expr* t2 = t1->get_expr();
             if ((c = compare_rec(n, binding, s, t2, evidence), c != l_undef)) {
                 evidence.push_back(euf::enode_pair(t1, tn));
diff --git a/src/sat/smt/q_eval.h b/src/sat/smt/q_eval.h
index 0ead01061fa..76c21934305 100644
--- a/src/sat/smt/q_eval.h
+++ b/src/sat/smt/q_eval.h
@@ -31,6 +31,7 @@ namespace q {
         euf::enode_vector  m_eval;
         euf::enode_vector  m_indirect_nodes;
         bool               m_freeze_swap = false;
+        euf::enode_pair    m_diseq_undef;
 
         struct scoped_mark_reset;