Re: [HoTT] Impredicative set + function extensionality + proof irrelevance consistent?

[Thorsten Altenkirch <Thorsten....@nottingham.ac.uk>]

On 15/12/2017, 17:00, "homotopyt...@googlegroups.com on behalf of
Thomas Streicher" <homotopyt...@googlegroups.com on behalf of
stre...@mathematik.tu-darmstadt.de> wrote:

>Moreover, toposes will not validate univalence. As pointed out to me
>by Martin Escardo you can't even formulate it because in arbitrary
>toposes you don't have universe (not to speak of univalent ones).

I was only talking about the special case of (-1)-univalence or
propositional extensionality that is for P,Q : Prop

(P <-> Q) -> (P = Q)

Thorsten
>





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