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For questions on limits and colimts in the sense of category theory, and related notions.

7 votes
1 answer
668 views

Finite coproducts commute with which limits in Set?

It is well known that (small) coproducts commute with connected limits in $\mathbf{Set}$. With which class of limits do finite coproducts commute? Ideally, we should furthermore like to know whether t …
varkor's user avatar
  • 10.7k
1 vote

Unexpected interaction between limits and colimits

My vague question is: given two diagrams in $D$, what comparisons between them induce a morphism of their limits? This is exactly the topic of Paré's paper Morphisms of Colimits: from Paths to Profu …
varkor's user avatar
  • 10.7k
3 votes
0 answers
109 views

Density with respect to a family of diagrams, versus a class of weights

In Theorem 5.19 of Kelly's Basic Concepts of Enriched Category Theory, it is proven that a fully faithful functor $K \colon \mathcal A \to \mathcal C$ is dense if and only if $\mathcal C$ is the closu …
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  • 10.7k
5 votes

Strongly compact categories (reference request)

Assuming $\mathcal C$ and $\mathcal D$ are locally small and $\mathcal C$ is small-cocomplete, a functor $F \colon \mathcal C \to \mathcal D$ is a left adjoint if and only if it is small-cocontinuous …
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  • 10.7k
11 votes

Is there a tricategory of bicategories and biprofunctors?

For those coming across this question more recently, there is now an answer to the original question. In fact, the tricategory of pseudoprofunctors has been defined twice, independently, via different …
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  • 10.7k
5 votes

Has the "Lambek embedding" into the category of (co)product-preserving presheaves been studi...

This construction is well known in enriched category theory, and has been studied in the increased generality of a class of weights (which recovers the finite discrete weights, describing finite (co)p …
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  • 10.7k
2 votes
Accepted

Weighted limits and Kan extension in Dist

I'm not sure I've followed your question exactly, so let me rephrase it to how I've understood it, and you can tell me if I've misunderstood. I shall use different letters to make sure I'm not acciden …
varkor's user avatar
  • 10.7k
11 votes
1 answer
440 views

Is every petite category essentially small?

A locally small category $\mathscr C$ is called petite if, for every functor $F : \mathscr C \to \mathscr D$ with locally small codomain, and for every object $D \in \mathscr D$, the presheaf $\mathsc …
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3 votes
0 answers
22 views

When does a lax monad morphism induce a functor between categories of algebras that preserve...

Let $S$ be a monad on a category $\mathbf C$. If $\mathbf C$ is cocomplete, and the category of algebras $\mathbf C^S$ admits reflexive coequalisers, then $\mathbf C^S$ is cocomplete. Thus, it is exis …
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  • 10.7k
8 votes
Accepted

Filtered 2-colimits commute with finite 2-limits

Two relevant papers are: Dupont's Interchange of filtered 2-colimits and finite 2-limits. Canevali's 2-filtered bicolimits and finite weighted bilimits commute in Cat. The former proves that finite …
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3 votes
1 answer
145 views

Examples of (co)lax idempotent pseudocomonads on Cat

A lax idempotent pseudomonad, also called a KZ doctrine or KZ monad, is a pseudomonad $(T, \mu, \eta)$ with the property that $T \eta \dashv \mu \dashv \eta T$. Lax idempotent pseudomonads were intro …
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  • 10.7k
4 votes
Accepted

Ends and coends – analogues for higher arity – Horn Filling

This is exactly the subject of the paper Coends of higher arity by Loregian and de Oliveira Santos.
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3 votes

Reference for certain categorical limits

We can view a category $C_0 \hookrightarrow C$ equipped with a specified subcategory as an $\mathscr M$-category, which is a category enriched in the category of injections and commutative squares. As …
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  • 10.7k
9 votes
0 answers
102 views

Cocompleteness of enriched categories of algebras

A useful result due to Linton is that for a cocomplete category $C$ and monad $T$ on $C$, if the category of algebras $C^T$ admits reflexive coequalisers, then it is cocomplete (see here for a sketch …
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8 votes
0 answers
161 views

Original reference for the Fam construction

For a category $\mathbf C$, the category of families of $\mathbf C$, denoted $\mathrm{Fam}(\mathbf C)$ is the free coproduct completion of $\mathbf C$. Explicitly, the objects of $\mathbf C$ are given …
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