fix bug in logic generation

gf/NGrammarLog.gf

@@ -30,7 +30,7 @@ concrete NGrammarLog of NGrammar = MCatsLog ** {
             postf = defi.postf;
         };
         def_mobj_is_mobj definiendum id definiens = {
-            pref = "∀" ++ "x0" ++ "." ++ (lwrap(definiens) ++ id.core ++ and_formula(id)) ++ "⇒" ++ "(" ++ lwrap(definiendum) ++ id.core;
+            pref = "∀" ++ id.core ++ "." ++ (lwrap(definiens) ++ id.core ++ and_formula(id)) ++ "⇒" ++ "(" ++ lwrap(definiendum) ++ id.core;
             postf = ")";
         };