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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 …
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 …
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 …
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 …
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 $C^*$ …
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 …
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 …
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 …
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 …
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 …
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 …
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 …
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 …
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 …
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 …