So it has to work in (at least) a three-valued logic, with the three values True, False, and I do not know.It is as if we can assume the value must be there is a place where lots of people go wrong: we can not make that assumption, it is just nonsense. (I think I am agreeing with you here.)The rest of this comment is a [n ex-] mathematical logician's take on Codd's work on having two sorts of N