CompuServe Messages

Tony I've finished a lisp I've been working on, save for a way around getting the dreaded "Bad entmod list". I'm using "(setq a1 (list (assoc -1 var)(cons 39 pck)))" to change thickness of an entity (& 40 height, 41 width, etc.). I havent't been able to figure out a way to prescreen "a1" so I can then divert a "bad" list from going through "(entmod a1)". I realize you can use an "initget", but in some cases this would be most impractical. If I could screen the a1, obviously I could then divert the entmod statement with an "if" statement. Such as if "pck=nil" then a bad entmod list will come up. There are other possibilities for "(entmod a1)" to come up with this message. I would like a "simple" way to catch these inputs before they crash the routine. Any suggestions on how determine this? Appreciatively, Jeff