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Algebraic varieties, stacks, sheaves, schemes, moduli spaces, complex geometry, quantum cohomology.

4 votes
0 answers
86 views

Efficient CW structures on squarefree semi-algebraic set

General Setup Given a collection of $k$ polynomials (with real coefficients) in $n$ real variables, say $f_i(x_1,\ldots,x_n)$, let $V \subset \mathbb{R}^n$ correspond to those $x$-values for which ev …
Vidit Nanda's user avatar
  • 15.5k
5 votes
Accepted

Simplicial complex construction from given Betti numbers?

One way to make things "minimal" (given the lack of any further information) is to construct a simplicial complex whose cup products are all trivial, so the (co)homology generators don't interact with …
Vidit Nanda's user avatar
  • 15.5k
11 votes

Why Cohen-Macaulay rings have become important in commutative algebra?

I'm no expert on the evolution of Cohen-Macaulay rings, so I will leave that part of your question for those who actually know their history. On a high level, Cohen-Macaulay rings are wonderful prec …
Vidit Nanda's user avatar
  • 15.5k
5 votes

Decomposition vs filtration vs stratification

At the risk of sounding (oxy?)moronic, I'd say that the term "stratification" is locally standard. Meaning, there exist (at least) three communities which agree internally on what the term means, but …
Vidit Nanda's user avatar
  • 15.5k
16 votes

Taking "Zooming in on a point of a graph" seriously

I haven't seen any Calculus books take this approach. Possibly, this is because it is not clear how to proceed in the case of functions that are not polynomials. Consider even the really nice function …
Vidit Nanda's user avatar
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16 votes
1 answer
359 views

Moduli space of boundary maps with prescribed chain and homology groups?

Let $R$ be a reasonable ring (maybe I mean a PID, or $\mathbb{Z}$, and when sufficiently desperate, a field). Now consider fixed sequences $C_n$ and $H_n$ of $R$-modules, which are tame in every possi …
Vidit Nanda's user avatar
  • 15.5k
12 votes

Can we define Whitney stratification algebraically?

There is a purely algebraic characterisation of Condition (B) due to Le and Teissier, see Proposition 1.3.8 of the paper Lê Dũng Tráng; Teissier, Bernard, Limites d’espaces tangents en géométrie analy …
Vidit Nanda's user avatar
  • 15.5k