As a point of interest, I've noticed that some of the code on AfraLISP mixes lower case "L" with the numeral "1", so you have to pay special attention if you're doing a cut/paste from the examples. The result is that it "looks" (as in this case) like "P1" but it's actually "Pl".
It shouldn't affect the OP's code any - just bringing it up because it will cause problems if you don't notice this and try to use the variable later on, but enter it incorrectly.
Edit: Sorry Chris, missed your note about the change!