[Agda] Re: Classical Mathematics for a Constructive World
Jan Burse
janburse at fastmail.fm
Sun Dec 2 12:01:22 CET 2012
Jan Burse schrieb:
> I get:
>
> P(x,z) -> forall y (C(x,y) -> Q(y,z))
>
> Question is now whether this implies:
>
> P(x,z)&R(z) -> forall y(C(x,y) -> Q(y,z)&R(z))
>
> I guess the answer is affirmative already in
> minimal logic. But I might be also wrong here.
Ramana Kumar just wrote me:
> The * is not just conjunction, it is separating
> conjunction. Maybe you know that already, but just
> to make sure, the semantics of P * R is (P * R)(x,h)
> = exists h1. exists h2. h = h1 + h2 & P(x,h1) & R(x,h2)
> where + is disjoint union. The choice issue is that the
> h2 for R on the Q * R side doesn't have to be the same.
In as far is this related to a choice principle? A
choice principle says whether a choice always exists
or not. It is not so much concerned with the stability
of a choice, that might or might not exists.
What is a typical counter example?
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