src/Pure/Syntax/syntax.ML

--- a/src/Pure/Syntax/syntax.ML	Thu Sep 21 19:04:12 2006 +0200
+++ b/src/Pure/Syntax/syntax.ML	Thu Sep 21 19:04:20 2006 +0200
@@ -462,7 +462,7 @@
 
     fun constify (ast as Ast.Constant _) = ast
       | constify (ast as Ast.Variable x) =
-          if x mem consts orelse NameSpace.is_qualified x then Ast.Constant x
+          if member (op =) consts x orelse NameSpace.is_qualified x then Ast.Constant x
           else ast
       | constify (Ast.Appl asts) = Ast.Appl (map constify asts);
   in