Hi, we have some continuous build tests that compile everything in safety 1 and safety 0. (Yeah, living on the edge, I know.) The latter fails the self-test for proper-list-length.2 If proper-list-length is called with an improper list of at least 1 cons, it signals an error. This is due to the explicit safety declaration in SAFE-ENDP. But if called on an atom, then memory corruption happens because SLOW is initialized sans type checks by (cons (car list) (cdr list)) What would be the intent in that case? To say to the user: "You're holding it wrong"? Thanks, Doug