fix #3822

Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>

src/muz/base/dl_context.h

@@ -528,6 +528,8 @@ namespace datalog {
          */
         model_ref get_model();
 
+        bool is_monotone();
+
         /**
            \brief retrieve proof from derivation of the query.