On ITS Maclisp, #+(NOT LISPM MACLISP) 3 reads as 3 #+(NOT MACLISP LISPM) 3 4 reads as 4 It just ignores the 2nd element. Syntax checking would be nice. Who knows but that someone might not think that #+(NOT a b c ...) means the same as #-(AND a b c ...) and lose ... -kmp