diff -r c0eaa8b9bff5 -r 3535f16d9714 src/Tools/Metis/src/ElementSet.sig
--- a/src/Tools/Metis/src/ElementSet.sig	Wed Jun 08 08:47:43 2011 +0200
+++ b/src/Tools/Metis/src/ElementSet.sig	Wed Jun 08 08:47:43 2011 +0200
@@ -131,6 +131,14 @@
 val disjoint : set -> set -> bool
 
 (* ------------------------------------------------------------------------- *)
+(* Closing under an operation.                                               *)
+(* ------------------------------------------------------------------------- *)
+
+val closedAdd : (element -> set) -> set -> set -> set
+
+val close : (element -> set) -> set -> set
+
+(* ------------------------------------------------------------------------- *)
 (* Converting to and from lists.                                             *)
 (* ------------------------------------------------------------------------- *)