src/Provers/order.ML

--- a/src/Provers/order.ML	Wed May 05 09:24:42 2010 +0200
+++ b/src/Provers/order.ML	Wed May 05 18:25:34 2010 +0200
@@ -871,8 +871,8 @@
       val vi = getIndex v ntc
 
   in
-      if ui mem xreachable andalso vi mem xreachable andalso
-         ui mem yreachable andalso vi mem yreachable then (
+      if member (op =) xreachable ui andalso member (op =) xreachable vi andalso
+         member (op =) yreachable ui andalso member (op =) yreachable vi then (
 
   (case e of (Less (_, _, _)) =>
        let