--- a/Set.st	Mon Aug 13 15:29:14 2012 +0200
+++ b/Set.st	Mon Aug 13 17:29:03 2012 +0200
@@ -13,7 +13,7 @@
 
 Collection subclass:#Set
 	instanceVariableNames:'tally keyArray'
-	classVariableNames:'DeletedEntry'
+	classVariableNames:'DeletedEntry NilEntry'
 	poolDictionaries:''
 	category:'Collections-Unordered'
 !
@@ -25,6 +25,13 @@
 	privateIn:Set
 !
 
+Object subclass:#NilKey
+	instanceVariableNames:''
+	classVariableNames:'TheOneAndOnlyInstance'
+	poolDictionaries:''
+	privateIn:Set
+!
+
 !Set class methodsFor:'documentation'!
 
 copyright
@@ -101,10 +108,13 @@
     "initialize the Set class"
 
     DeletedEntry isNil ifTrue:[
-	DeletedEntry := EmptySlot new
+        DeletedEntry := EmptySlot new.
+        NilEntry := NilKey new.
     ].
 
-    "Set initialize"
+    "
+        Set initialize
+    "
 
     "Modified: 24.1.1997 / 21:09:00 / cg"
 ! !
@@ -1083,6 +1093,7 @@
     ^ tally
 ! !
 
+
 !Set methodsFor:'testing'!
 
 capacity 
@@ -1181,14 +1192,25 @@
 
 ! !
 
+!Set::NilKey class methodsFor:'instance creation'!
+
+basicNew
+    TheOneAndOnlyInstance isNil ifTrue:[
+        TheOneAndOnlyInstance := super basicNew
+    ].
+    ^ TheOneAndOnlyInstance
+
+
+! !
+
 !Set class methodsFor:'documentation'!
 
 version
-    ^ '$Header: /cvs/stx/stx/libbasic/Set.st,v 1.112 2012-08-04 18:34:26 cg Exp $'
+    ^ '$Header: /cvs/stx/stx/libbasic/Set.st,v 1.113 2012-08-13 15:29:03 stefan Exp $'
 !
 
 version_CVS
-    ^ '$Header: /cvs/stx/stx/libbasic/Set.st,v 1.112 2012-08-04 18:34:26 cg Exp $'
+    ^ '$Header: /cvs/stx/stx/libbasic/Set.st,v 1.113 2012-08-13 15:29:03 stefan Exp $'
 ! !
 
 Set initialize!