Virgil
Posts:
7,005
Registered:
1/6/11


Re: A finite set of all naturals
Posted:
Aug 17, 2013 1:14 AM


In article <usDPt.85898$An7.26389@fx08.iad>, Nam Nguyen <namducnguyen@shaw.ca> wrote:
> On 16/08/2013 1:33 PM, Virgil wrote: > > In article <c10s09pu0gs0av09l4gfqrrpbdm5gj510n@4ax.com>, > > quasi <quasi@null.set> wrote: > > > >> quasi wrote: > >>> > >>> Or how about the following instead? > >>> > >>> odd(x) <> [x*y=2*z] > Ew[y=2*w] > >> > >> to Nam: > >> > >> Since you've has already defined various versions of even(x), > >> my above definition of odd(x) can be expressed more simply as: > >> > >> odd(x) <> even(x*y) > even(y) > >> > >> Doesn't that qualify as a "positive formula"? > > No. Like Ben's D2, it's a "negative" formula. > > >> > >> quasi > > > > I like that one! > > If you say so. One of course can "like" anything as one wishes, > including a "negative" formula.
If implication does not make it negative, which you seem to allow elsewhere, wherein does your alleged negative appear in it? 

