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

7 votes
1 answer
607 views

Name for vector spaces with two algebra structures that satisfy the exchange law

Is there a name/reference for the following object? We have a vector space $V$ over some field with two associative bilinear operations $\circ,*:V \times V \to V$ which satisfy the interchange law, i. …
Vidit Nanda's user avatar
  • 15.5k
21 votes
3 answers
1k views

Are functor categories with triangulated codomains themselves triangulated?

I'm fairly confident that the following assertion is true (but I will confess that I did not verify the octahedral axiom yet): Let $T$ be a triangulated category and $C$ any category (let's say small …
Vidit Nanda's user avatar
  • 15.5k
5 votes
1 answer
146 views

Equivalence generated by Jacobian minors

Let $f,g:\mathbb{R}^m \to \mathbb{R}^n$ be two smooth functions and let $k$ be a strictly positive integer. Write $f \sim_k g$ if at each point in the domain, the determinants of all $k \times k$ mino …
Vidit Nanda's user avatar
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1 vote
Accepted

Confluent partial orders

In a context slightly more general than yours, this is called the right Ore condition. If you treat your poset as a category where there is a unique morphism from $p$ to $q$ if and only if $p \geq q$ …
Vidit Nanda's user avatar
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37 votes
Accepted

Reference on Persistent Homology

Since this area is developing rather quickly, there is a dearth of canonical references that would satisfy basic pedagogical requirements. If I were teaching a course on this material right now, I wou …
Vidit Nanda's user avatar
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5 votes
Accepted

What functions have the same persistence diagrams?

Your question is precisely the subject of Justin Curry's recent preprint. Bottom line: if you agree to identify functions $f,g:[0,1] \to \mathbb{R}$ whenever they have the same merge-tree, then ther …
Vidit Nanda's user avatar
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3 votes

discrete Grothendieck construction

The name of that article changed (a lot, it seems): the information you seek is in the paper Doctrinal Adjunction by Kelly. It lies on page 257 of the collection Category Seminar, Number 420 of Le …
Vidit Nanda's user avatar
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7 votes
Accepted

Who first considered constructibility of simplicial complexes?

If you want the first use of the term "constructible" in this context, then your reference to Mel Hochster's work is right-on. But if you want the actual notion, then things get slightly hazy. I think …
Vidit Nanda's user avatar
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7 votes
Accepted

Homotopy theory of acyclic categories

Here is a cool new (and very readable) preprint which uses the second barycentric subdivision (as discussed in Zhen Lin, Fernando Muro and Peter May's comments) to construct a cofibrantly generated mo …
Vidit Nanda's user avatar
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7 votes

Between Tietze's and Dugundji's extension theorems

Bad News The answer to Q3 as stated is no. Let $X$ be the Michael line, and let $Y$ be the closed subset consisting of all the rationals. Then, there is no bounded linear extension $C(Y,\mathbb{R}) \t …
Vidit Nanda's user avatar
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2 votes

Using Discrete Morse Theory to represent hom classes

The answer to your question as stated is no. What discrete Morse theory gives you, starting from a finite regular CW complex $X$ and a discrete Morse function $f:X \to \mathbb{R}$ (with discrete vec …
Vidit Nanda's user avatar
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3 votes
2 answers
666 views

Zigzags and contractibility of categories

Let $\mathbf{C}$ be a small category and $\mathbf{C}'$ its hammock localization in the sense of Dwyer and Kan. I am looking for a proof (or counterexample) of the following assertion: If there is …
Vidit Nanda's user avatar
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10 votes
1 answer
283 views

Localizing 2-categories about a single morphism

This question is a straight-up reference request, but of course I will be grateful for an answer in the event that no references are readily available. Consider a strict $2$-category $\mathbf{C}$ and …
Vidit Nanda's user avatar
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8 votes
1 answer
412 views

Areas of Triangles in (Non-Riemannian) Metric spaces?

I'm looking for a reasonable way to coherently axiomatize both length and area in the absence of a Riemannian structure, i.e., starting only with a metric space; but it's not clear how much of this wo …
Vidit Nanda's user avatar
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7 votes
2 answers
1k views

What's an initial object in a poset-enriched category?

I have a functor $F:C \to D$ between poset-enriched categories, and I'd like to show that the induced map on classifying spaces is a homotopy-equivalence. To this end, I am trying to establish the pre …
Vidit Nanda's user avatar
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