--- a/Change.st	Tue Feb 07 13:48:56 2017 +0100
+++ b/Change.st	Fri Feb 10 11:16:53 2017 +0100
@@ -48,6 +48,16 @@
 "
 ! !
 
+!Change class methodsFor:'queries'!
+
+isAbstract
+    "Return if this class is an abstract class.
+     True is returned here for myself only; false for subclasses.
+     Abstract subclasses must redefine this again."
+
+    ^ self == Change.
+! !
+
 !Change class methodsFor:'support'!
 
 isSource:source1Arg sameSourceAs:source2Arg