diff --git a/src/muz/rel/dl_compiler.cpp b/src/muz/rel/dl_compiler.cpp
index 9e8ead241..59ba260a4 100644
--- a/src/muz/rel/dl_compiler.cpp
+++ b/src/muz/rel/dl_compiler.cpp
@@ -85,7 +85,7 @@ namespace datalog {
             removed_cols.size(), removed_cols.c_ptr(), result));
     }
 
-    void compiler::make_select_equal_and_project(reg_idx src, const relation_element & val, unsigned col,
+    void compiler::make_select_equal_and_project(reg_idx src, const relation_element val, unsigned col,
             reg_idx & result, bool reuse, instruction_block & acc) {
         relation_signature res_sig;
         relation_signature::from_project(m_reg_signatures[src], 1, &col, res_sig);
@@ -139,7 +139,7 @@ namespace datalog {
         return r;
     }
 
-    compiler::reg_idx compiler::get_single_column_register(const relation_sort & s) {
+    compiler::reg_idx compiler::get_single_column_register(const relation_sort s) {
         relation_signature singl_sig;
         singl_sig.push_back(s);
         return get_fresh_register(singl_sig);
@@ -165,7 +165,7 @@ namespace datalog {
         }
     }
 
-    void compiler::make_add_constant_column(func_decl* head_pred, reg_idx src, const relation_sort & s, const relation_element & val,
+    void compiler::make_add_constant_column(func_decl* head_pred, reg_idx src, const relation_sort s, const relation_element val,
             reg_idx & result, bool & dealloc, instruction_block & acc) {
         reg_idx singleton_table;
         if(!m_constant_registers.find(s, val, singleton_table)) {
@@ -185,7 +185,7 @@ namespace datalog {
         }
     }
 
-    void compiler::make_add_unbound_column(rule* compiled_rule, unsigned col_idx, func_decl* pred, reg_idx src, const relation_sort & s, reg_idx & result, 
+    void compiler::make_add_unbound_column(rule* compiled_rule, unsigned col_idx, func_decl* pred, reg_idx src, const relation_sort s, reg_idx & result,
             bool & dealloc, instruction_block & acc) {
         
         TRACE("dl", tout << "Adding unbound column " << mk_pp(pred, m_context.get_manager()) << "\n";);
@@ -862,9 +862,11 @@ namespace datalog {
         ast_manager& m = m_context.get_manager();
         unsigned pt_len = r->get_positive_tail_size();
         unsigned ut_len = r->get_uninterpreted_tail_size();
-        if (pt_len == ut_len) {
+
+        // no negated predicates
+        if (pt_len == ut_len)
             return;
-        }
+
         // populate negative variables:
         for (unsigned i = pt_len; i < ut_len; ++i) {
             app * neg_tail = r->get_tail(i);
diff --git a/src/muz/rel/dl_compiler.h b/src/muz/rel/dl_compiler.h
index 8c33f987c..4902b9387 100644
--- a/src/muz/rel/dl_compiler.h
+++ b/src/muz/rel/dl_compiler.h
@@ -135,7 +135,7 @@ namespace datalog {
 
         reg_idx get_fresh_register(const relation_signature & sig);
         reg_idx get_register(const relation_signature & sig, bool reuse, reg_idx r);
-        reg_idx get_single_column_register(const relation_sort & s);
+        reg_idx get_single_column_register(const relation_sort s);
 
         /**
            \brief Allocate registers for predicates in \c pred and add them into the \c regs map.
@@ -150,7 +150,7 @@ namespace datalog {
             const unsigned_vector & removed_cols, reg_idx & result, bool reuse_t1, instruction_block & acc);
         void make_filter_interpreted_and_project(reg_idx src, app_ref & cond,
             const unsigned_vector & removed_cols, reg_idx & result, bool reuse, instruction_block & acc);
-        void make_select_equal_and_project(reg_idx src, const relation_element & val, unsigned col,
+        void make_select_equal_and_project(reg_idx src, const relation_element val, unsigned col,
             reg_idx & result, bool reuse, instruction_block & acc);
         /**
            \brief Create add an union or widen operation and put it into \c acc.
@@ -174,10 +174,10 @@ namespace datalog {
 
         void make_dealloc_non_void(reg_idx r, instruction_block & acc);
 
-        void make_add_constant_column(func_decl* pred, reg_idx src, const relation_sort & s, const relation_element & val,
+        void make_add_constant_column(func_decl* pred, reg_idx src, const relation_sort s, const relation_element val,
             reg_idx & result, bool & dealloc, instruction_block & acc);
 
-        void make_add_unbound_column(rule* compiled_rule, unsigned col_idx, func_decl* pred, reg_idx src, const relation_sort & s, reg_idx & result, 
+        void make_add_unbound_column(rule* compiled_rule, unsigned col_idx, func_decl* pred, reg_idx src, const relation_sort s, reg_idx & result,
             bool & dealloc, instruction_block & acc);
         void make_full_relation(func_decl* pred, const relation_signature & sig, reg_idx & result, 
             instruction_block & acc);