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Homotopy theory, homological algebra, algebraic treatments of manifolds.

19 votes
0 answers
773 views

Folk Functorial Figuring

In the CRM Proceedings & Lecture Notes Volume 50 "A Celebration of the Mathematical Legacy of Raoul Bott" Herbert Shulman writes (p. 48): "[Bott] taught many of us to think functorially, like thin …
Justin Curry's user avatar
  • 2,684
23 votes
5 answers
5k views

Stiefel-Whitney Classes over Integers?

An interesting thing happened the other day. I was computing the Stiefel-Whitney numbers for $\mathbb{C}P^2$ connect sum $\mathbb{C}P^2$ to show that it was a boundary of another manifold. Of course, …
Justin Curry's user avatar
  • 2,684
17 votes
4 answers
3k views

Group Structure on CP^infinty

I was inspired by the following algebraic topology orals question: "Is $S^1$ the loop space of another space?" This is easy to see if you recognize that $S^1$ is a $K(\mathbb{Z},1)$, and the loop sp …
Justin Curry's user avatar
  • 2,684
2 votes

Understanding (the wiki page on) Verdier duality

I just revamped what was written. Perhaps now it is more understandable:New Wiki Entry on Verdier duality.
Justin Curry's user avatar
  • 2,684
20 votes
1 answer
2k views

Every Manifold Cobordant to a Simply Connected Manifold

I am wondering if it is true that every compact, connected, oriented manifold is cobordant to a simply connected manifold. I believe that some sort of surgery will do the trick. Roughly speaking, I w …
Justin Curry's user avatar
  • 2,684
5 votes
1 answer
456 views

Derived Equivalence of Sheaves and Homotopy

This question loosely elaborates on an earlier question. It is pretty silly, but I'd like to hear some authoritative answers. Recall that if $f:S^{\bullet}\to T^{\bullet}$ is a quasi-isomorphism of s …
Justin Curry's user avatar
  • 2,684
15 votes

Cosheaf homology and a theorem of Beilinson (in a paper on Mixed Tate Motives)

Cosheaves are indeed mysterious gadgets. On the one hand, cosheaves are everywhere, but on the other hand, someone used to thinking sheaf-theoretically may have some problems. I am very close to finis …
Justin Curry's user avatar
  • 2,684
6 votes
3 answers
2k views

Segal's Original Definition of a Topological Category

Nowadays we can associate to a topological space $X$ a category called the fundamental (or Poincare) $\infty$-groupoid given by taking $Sing(X)$. There are many different categories that one can asso …
Justin Curry's user avatar
  • 2,684
7 votes

Two kinds of orientability/orientation for a differentiable manifold

Also I ask, are there any additional ways to define orientability/orientation for a differentiable manifold(not just for a vector space)? Another notion of orientability is the existence of an at …
Justin Curry's user avatar
  • 2,684
14 votes

PDE on manifolds

There are lots of possible answers to your question, but maybe here are some ideas. They aren't papers, but good projects. Method of Characteristics in First Order Nonlinear PDE can be interpreted v …
Justin Curry's user avatar
  • 2,684
13 votes
3 answers
2k views

Representations of \pi_1, G-bundles, Classifying Spaces

This question is inspired by a statement of Atiyah's in "Geometry and Physics of Knots" on page 24 (chapter 3 - Non-abelian moduli spaces). Here he says that for a Riemann surface $\Sigma$ the first …
Justin Curry's user avatar
  • 2,684
4 votes

Homotopy property of constructible sheaves on stratified spaces

Here are two comments: 1) I suspect the answer is "yes," so long as your homotopy has the property that your pullback is locally constant (and hence, by triviality of the interval, constant) along th …
Justin Curry's user avatar
  • 2,684