That !0 == 1 is not "well-defined" that I've noticed - perhaps someone could point out precisely where this is stated in a way that is not only definitive, but unambivalent (e.g., I don't want to see docs saying "It works this way, but don't trust it.").

I can still remember Drew Sullivan, currently GTALUG President, pointing out years ago that !!!0 == 1 works, even if !0 == 1 is not necessarily accurate.