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Enriched categories, topoi, abelian categories, monoidal categories, homological algebra.
61
votes
8
answers
7k
views
Natural transformations as categorical homotopies
Every text book I've ever read about Category Theory gives the definition of natural transformation as a collection of morphisms which make the well known diagrams commute.
There is another possible d …
41
votes
Is Mac Lane still the best place to learn category theory?
I doubt that someone could learn higher category theory (and more in general higher dimensional algebra) without first studying a little of category theory, mostly because the definition given in such …
21
votes
3
answers
3k
views
Relation between monads, operads and algebraic theories
I've begun to interest in algebraic theories and their categorical models: in particular monads, generalized multicategories and operads, lawvere theories and their generalization. Is there any refere …
20
votes
5
answers
3k
views
Computations in $\infty$-categories
Direct to the point.
Since now I've looked a lot of presentations of $\infty$-categories, but it seems that the only way to do explicit computations on these objects is via model categories. Is that s …
13
votes
Accepted
Categories presented with Arrows only, no objects: partial monoids
Of course you can define a (just-arrow) category $\mathcal C$ like a partial algebra which consist of:
a set $\mathcal C$ (namely the set of arrows of your category), a set $D_\mathcal{C} \subseteq \ …
9
votes
Why did Voevodsky consider categories "posets in the next dimension", and groupoids the corr...
I cannot say what exactly Voevodsky meant but here is a wild guess.
Disclaimer in what follows I use heavily type theoretic notation, so you have trouble understanding feel free to ask in the comment …
8
votes
3
answers
3k
views
What is higher dimensional algebra?
Could anyone explain what higher dimensional algebra is?
I tried to look on the web but I couldn't find a satisfactory definition, the ones that I found are too vague. What I'm looking for is a good …
7
votes
Multicategories vs Categories
Is there a way to recapture the additional understanding imparted by multicategories using higher categories?
Well I would say so. Multicategories are basically categories whose morphisms have multi …
6
votes
Category theorists stance on deductive systems
I think the idea should pretty much like this: once you drop the requirement for the deductive system to be freely generated from the axioms by the inference rules (i.e. you accept the existence of no …
6
votes
3
answers
2k
views
Monad arising from operad
It's known that from every operad arises a cartesian monad whose algebras are the algebras for the operad. Leinster proved that there are different operads from which arise the same monad, in this way …
5
votes
What is the difference between a function and a morphism?
Another interesting reason why categories cannot be identified always with categories having functions for morphisms is given in this paper, by Peter Freyd in which is proven that there are some categ …
5
votes
Accepted
Motivation/intuition behind the definition of delta-functors and related concepts
I am not an expert on the subject but looking at the definition I would dare to say that these are basically the axioms that characterize an homology theory, if it weren't for the fact the $\delta$ ma …
4
votes
Natural transformations as categorical homotopies
Following the previous indication of Professor Brown I want to add another possible way to see natural transformation which is a generalization of the previous definition.
Given categories $\mathc …
4
votes
The symmetric monoidal closed structure on the category of $\mathcal{F}$-cocomplete categori...
I am not aware of Kock's works.
Nevertheless Kelly provides the definition of its tensor product in the next page: it defines its tensor product $\mathcal A \otimes_{\mathcal F} \mathcal B$ as the $\ …
4
votes
2
answers
646
views
Equivalence in $\infty$-categories
In every $n$-category (weak or strict) can be defined the concept of equivalence via a recursive definition:
* an equivalence in a set ($0$-category) is just an identity;
* for each $n \in \mathbb N$ …