--- a/DisplayTransform.st	Fri Feb 10 11:17:50 2017 +0100
+++ b/DisplayTransform.st	Fri Feb 10 11:18:11 2017 +0100
@@ -1,5 +1,3 @@
-"{ Encoding: utf8 }"
-
 "{ Package: 'stx:libview' }"
 
 "{ NameSpace: Smalltalk }"
@@ -37,6 +35,16 @@
 	^self new setIdentity
 ! !
 
+!DisplayTransform 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 == DisplayTransform.
+! !
+
 !DisplayTransform methodsFor:'accessing'!
 
 inverseTransformation