The error message says that the Rexx interpreter thinks that you have a colon (:) after your A. To find what the 'not' operator is you have access to manuals including the Rexx Language Reference. That information is in there. Do not connfuse what might be legal on the PC with what might be legal on the mainframe. To be portable you should use <>. Ususally on the mainframe you use the symbol usually found on the top of the top left key - accessed via Alt Gr in Windoze.
And, please do not colour code your posts - using the full editor you can highlight your code and click the 'Code' button. This will preserve spacing and give you a nice blue on black presentation like this..
The problem I have is that people can explain things quickly but I can only comprehend slowly.