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This tag is used if a reference is needed in a paper or textbook on a specific result.

1 vote
Accepted

Reference: uniformity of pointwise convergence has no countable base

If it is not in bourbaki, I don't have a reference in mind, but here is a proof : Let $(B_n)$ for $n \in \mathbb{N}$ be any countable family of entourage. Then because each $B_n$ is an entourage one …
Simon Henry's user avatar
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16 votes
Accepted

Are equivalences of categories stable under filtered colimits?

For filtered diagram (as asked in the question) the answer is yes. Of course this fails for general diagram as mentioned in Harry's answer. Of course the "equivalence" has to be implemented by a pseud …
Simon Henry's user avatar
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3 votes
Accepted

Categories admitting singleton-classifiers and characterization of the category $\mathbf{Set}$

I don't think this has been considered. Mainly I've never seen it, but also there are specific feature of this notions that makes it unlikely to be a relevant category theoretic notion independently o …
Simon Henry's user avatar
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9 votes
1 answer
172 views

Reference request: a lemma on universes and polynomial monads

I'm looking for a reference that covers things like the lemma below - it doesn't have to be the exact statement I'm going to give, anything in the general ballpark would probably be useful. Or if you …
Simon Henry's user avatar
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7 votes
1 answer
479 views

Two notions of bundle of C* algebras

One can find in the literature two notions of $C^*$-algebra over a topological space $X$. The first is as the data of an open surjection $ \pi: B \rightarrow X$ together with the structure of a $C^*$ …
Simon Henry's user avatar
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6 votes
1 answer
175 views

Propositional vs Definitional extentionality in type theory

There are essentially two ways to impose extentionality on a type theory (I know, it is not very fashionable to impose extentionality these days, but please, bear with me) you can either have a "propo …
Simon Henry's user avatar
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4 votes
0 answers
134 views

References for a lemma about compact operators on a Hilbert module

I am looking for a reference for the following result: If $A$ and $B$ are C* algebras, $H$ is a right Hilbert $A$-modules, $\phi :A \rightarrow B$ is a morphism, and assume that there is a map $\eta …
Simon Henry's user avatar
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6 votes
1 answer
211 views

References requestion : Pretopos are algebras for a composed monad?

Unless I'm mistaken the "Free completion under finite limits monad" $C \mapsto C^{lex}$ and the "free co-completion monad" $C \mapsto \widehat{C}$ (the categories of small presheaves) satisfies a dist …
Simon Henry's user avatar
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4 votes

Do hom-sets really live in the category Set?

I think the question is vague and probably does not have a unique answer. I would says that this kind of concern is actually not so different from the "size issue " generally presented by the set of …
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6 votes
0 answers
464 views

The topos of a graph

If $G$ is, for example, a finite directed graph, one can attach to it a topos $T_G$ whose objects are "$G$-sheaves". A $G$-sheave $F$ is the data of: For each verticies $x$ a set $F(x)$, for each arr …
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2 votes
Accepted

Extending a monoid object in a category

I don't think the question as you asked with the construction you are describing as been explicitely treated in the literature (though it very well could be). What has been discused a lot in the litte …
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6 votes
0 answers
180 views

(Reference Request) Tensor product of chain complexes in terms of strict $\infty$-categories

(note: this question is essentially a reference request for the tensor product described at the end. the rest is context) It is well known that the category of chain complexes (in positive degree, wi …
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22 votes
Accepted

Why is the theory of small categories not algebraic?

This follows from two Facts: 1) A category monadic over Set/S is always an exact category. That is it has quotient by equivalence relation that are effective and universal. It is in particular a regu …
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3 votes
Accepted

Universal model category as a $\text{sSet}$-enriched co-completion

Given $C$ a small category (eventually, a small simplicial category) I denote by $UC$ the projective model structure on the category of simplicial presheaves on $C$ as in the paper. Using the kind of …
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5 votes
Accepted

Is every folk cofibration of strict $\omega$-categories a monomorphism?

I just thought (or maybe remember) a neat proof of this fact. It involve ideas I worked on a few years ago but never published - but that's short enough so that I can explain the key ideas on MO. Let …
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