--- a/AbstractNumberVector.st	Sun Mar 24 12:27:09 2019 +0100
+++ b/AbstractNumberVector.st	Sun Mar 24 12:29:29 2019 +0100
@@ -52,6 +52,14 @@
 
 !AbstractNumberVector 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 == AbstractNumberVector.
+!
+
 maxVal
     "the maximum value which can be stored in instances of me"