diff -r 2024d9f7df9c -r ffbc5a57191a src/Pure/Thy/thm_deps.ML
--- a/src/Pure/Thy/thm_deps.ML	Thu Sep 21 19:04:12 2006 +0200
+++ b/src/Pure/Thy/thm_deps.ML	Thu Sep 21 19:04:20 2006 +0200
@@ -54,7 +54,7 @@
                     | NONE => [])
                  | _ => ["global"]);
             in
-              if name mem parents' then (gra', parents union parents')
+              if member (op =) parents' name then (gra', parents union parents')
               else (Symtab.update (name,
                 {name = Sign.base_name name, ID = name,
                  dir = space_implode "/" (session @ prefx),