diff --git a/src/muz/dataflow/dataflow.h b/src/muz/dataflow/dataflow.h
index 9e100121a..1e52c5f93 100644
--- a/src/muz/dataflow/dataflow.h
+++ b/src/muz/dataflow/dataflow.h
@@ -87,6 +87,7 @@ namespace datalog {
             for (func_decl_set::iterator I = output_preds.begin(),
                 E = output_preds.end(); I != E; ++I) {
                 func_decl* sym = *I;
+                TRACE("dl", tout << sym->get_name() << "\n";);
                 const rule_vector& output_rules = m_rules.get_predicate_rules(sym);
                 for (unsigned i = 0; i < output_rules.size(); ++i) {
                     m_facts.insert_if_not_there2(sym, Fact())->get_data().m_value.init_down(m_context, output_rules[i]);
diff --git a/src/muz/transforms/dl_mk_coi_filter.cpp b/src/muz/transforms/dl_mk_coi_filter.cpp
index 67b88724c..c452e2611 100644
--- a/src/muz/transforms/dl_mk_coi_filter.cpp
+++ b/src/muz/transforms/dl_mk_coi_filter.cpp
@@ -41,6 +41,9 @@ namespace datalog {
             bool new_tail = false;
             bool contained = true;
             for (unsigned i = 0; i < r->get_uninterpreted_tail_size(); ++i) {
+                if (m_context.has_facts(r->get_decl(i))) {
+                    return 0;
+                }
                 if (r->is_neg_tail(i)) {
                     if (!engine.get_fact(r->get_decl(i)).is_reachable()) {
                         if (!new_tail) {