Date: Thu, 12 Nov 2009 19:55:40 -0800 From: Thomas Bushnell BSG <tb@xxxxxxxxxx> What do you expect procedure-arity to return for a procedure which accepts any number of arguments? IEEE +inf? -1, presumably. The numerical value isn't significant; its representation as a bit string in two's-complement is what matters, and for -1 that is a bit string of all ones.