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Enriched categories, topoi, abelian categories, monoidal categories, homological algebra.
8
votes
2
answers
469
views
Reference request: (co)limits in Eilenberg--Moore (V-)categories
The following result seems to be well known:
If T is a (V-)monad on a (V-)category C, then the forgetful functor $U^T \colon C^T \to C$ creates
any limits that exist in C, and
any colimits that exis …
15
votes
Accepted
Any example of a non-strong monad?
Here is a class of examples different to Tom's: if your underlying monoidal category C is closed, then a strong monad on C is the same as a C-enriched monad, i.e. one that respects the enrichment of C …
27
votes
morita equivalence for categories
That their Cauchy completions are equivalent.
4
votes
Accepted
Category enriched over a monoidal 2-category
Yes, here: R. Garner, M. Shulman, Enriched categories as a free cocompletion. arxiv.
4
votes
Kan extensions of pseudofunctors
I haven't seen this written down anywhere, but I've worked it out myself in a paper I'm working on. The paper isn't quite ready, so I'll just sketch the idea here.
As Zhen says, you need to generali …
2
votes
Accepted
Functor generalisation
Here is one way to look at it: if V is a monoidal category and $\mathbf{B} V$ is the corresponding one-object bicategory, then a V-category in the usual sense is the same thing as a lax functor $\math …
2
votes
Basic category theory: Universality of adjunction unit is justified by Yoneda Proposition in...
Our adjunction isomorphism $\phi$ does not necessarily involve the assignment above.
Yes, it does, by Yoneda's lemma. The bijection $\phi$ is natural, hence its value $\eta_x$ at the identity de …
8
votes
Accepted
A question on the Grothendieck construction
The bicategory of elements of a Cat-valued functor is defined in e.g. Street's Fibrations in bicategories; it's the same as the usual one, with 2-cells as described here. Its property of classifying …
5
votes
Ends and coends as Kan extensions (without using the subdivision category of Mac Lane)?
I don't know of any definition involving Kan extensions, but (co)ends can be expressed as (co)limits weighted by a hom functor (see e.g. here), so that for $F \colon C^{op} \times C \to D$ the end $\i …
5
votes
Categorification of coends and ends
I don't think I have seen anything like this published before, but I have written up a similar definition here (see here too).
One thing in your definition I would take issue with is that your 2-coen …
3
votes
Codomain fibration.
I assume that by 'cartesian' you mean 'having cartesian products'. In that case the answer is no. You've more or less said this yourself: for $C^{\mathbf{3}} \to C^{\mathbf{2}}$ or the composite $C^ …
5
votes
Monadicity and sheaves.
The answer (to the first question) is yes: reflections are always monadic, and the associated monad is idempotent.
21
votes
The main theorems of category theory and their applications
Monadicity theorems like Beck's give sufficient conditions on a functor $U \colon B \to A$ with a left adjoint F to be equivalent (in the slice category Cat/A) to the forgetful functor out of the cate …
11
votes
The main theorems of category theory and their applications
There was some discussion here about special cases of Yoneda's lemma, including the usual examples of Cayley's theorem for groups and Dedekind's embedding theorem for posets.
It also seems that a goo …
14
votes
Is there a nice application of category theory to functional/complex/harmonic analysis?
First, a disclaimer: I am not even close to being an analyst. Second, I don't know of any applications of category theory to the areas of analysis that you mention. I don't think we have got to that …