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Stream: learning: questions

Topic: Is the opposite of a closed category closed?


view this post on Zulip Asad Saeeduddin (Apr 05 2020 at 02:45):

Given a category CC that is closed under an internal hom functor [,][-, -], is the category CopC^{op} also closed under some internal hom?

view this post on Zulip Asad Saeeduddin (Apr 05 2020 at 02:51):

Sorry, let me amend the question. Given a category that is closed monoidal (i.e. having a monoidal structure, an internal hom functor, and an adjunction between the tensor and the hom), is the opposite category also a) closed, and b) closed-monoidal?

view this post on Zulip Asad Saeeduddin (Apr 05 2020 at 02:53):

The opposite category is definitely monoidal under the same tensor, and FG    GopFop\mathcal{F} \dashv \mathcal{G} \implies \mathcal{G}^{op} \dashv \mathcal{F}^{op} I believe

view this post on Zulip Christian Williams (Apr 05 2020 at 04:49):

Yes, that's right. Nice, I've never thought about this before. Any particular motivation?

view this post on Zulip sarahzrf (Apr 05 2020 at 04:57):

wait, what's the hom

view this post on Zulip sarahzrf (Apr 05 2020 at 04:57):

wouldnt it be coclosed

view this post on Zulip Christian Williams (Apr 05 2020 at 05:09):

Oh! Good point, now the "hom" is a left adjoint. Where have you come across the notion of coclosed?

view this post on Zulip sarahzrf (Apr 05 2020 at 05:59):

one time i was questioning whether the opposite of a topos could be a topos and "cocartesian coclosed" came up

view this post on Zulip John Baez (Apr 05 2020 at 06:29):

The only place I've seen it is in co-Heyting algebras, where "or" has a left adjoint.

view this post on Zulip James Wood (Apr 05 2020 at 09:40):

Cocartesian closed categories really suck (https://ncatlab.org/nlab/show/cocartesian+closed+category), but yeah, cocartesian coclosed categories make sense.

view this post on Zulip Asad Saeeduddin (Apr 06 2020 at 12:14):

@Christian Williams In programming people like working with the "closed functor" representations more frequently than the "monoidal functor" representation for whatever reason, and I was trying to port some facts to the opposite category