quasi
Posts:
11,066
Registered:
7/15/05


Re: A finite set of all naturals
Posted:
Aug 23, 2013 5:03 AM


Peter Percival wrote: >Nam Nguyen wrote: >> >> I certainly meant "odd(x) can _NOT_ be defined as a >> positive formula ...". > >Prove it.
With Nam's new definition of positive/negative, I think it's immediately provable (subject to some clarification as to what a formula is) that odd(x) is a negative formula.
Let even(x) <> Ey(x=2*y).
Assuming Nam's definition of "formula" supports the claim that even(x) is a positive formula, then odd(x) must be a negative formula since odd(x) is equivalent to ~even(x).
So, conceding that, where does he go with it?
quasi

