Ask for reason why a smt prover response unknown only for counterexamples.

src/printer/smtv2.ml

@@ -582,8 +582,10 @@ let print_prop_decl vc_loc cntexample args info fmt k pr f = match k with
       let model_list = S.elements info.info_model in
       fprintf fmt "@[(check-sat)@]@\n";
       print_info_model cntexample fmt model_list info;
-      (* (get-info :reason-unknown) *)
-      fprintf fmt "@[(get-info :reason-unknown)@]@\n";
+      if cntexample then begin
+	(* (get-info :reason-unknown) *)
+	fprintf fmt "@[(get-info :reason-unknown)@]@\n";
+      end;
 
       args.printer_mapping <- { lsymbol_m = args.printer_mapping.lsymbol_m;
 				vc_term_loc = vc_loc;