src/Tools/Code/code_thingol.ML

    of SOME class => thyname_of_class thy class
     | NONE => (case Code.get_type_of_constr_or_abstr thy c
        of SOME (tyco, _) => Codegen.thyname_of_type thy tyco
         | NONE => Codegen.thyname_of_const thy c);
   fun purify_base "==>" = "follows"
+    | purify_base "==" = "meta_eq"
     | purify_base s = Name.desymbolize false s;
   fun namify thy get_basename get_thyname name =
     let
       val prefix = get_thyname thy name;
       val base = (purify_base o get_basename) name;