src/Pure/Isar/session.ML

--- a/src/Pure/Isar/session.ML	Thu Sep 21 19:04:12 2006 +0200
+++ b/src/Pure/Isar/session.ML	Thu Sep 21 19:04:20 2006 +0200
@@ -50,7 +50,7 @@
 (* init *)
 
 fun init reset parent name =
-  if not (parent mem_string (! session)) orelse not (! session_finished) then
+  if not (member (op =) (! session) parent) orelse not (! session_finished) then
     error ("Unfinished parent session " ^ quote parent ^ " for " ^ quote name)
   else (add_path reset name; session_finished := false);