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Homotopy theory, homological algebra, algebraic treatments of manifolds.
10
votes
Accepted
Kontsevich integral : state of the art
I don't think that there has been a tremendous amount of progress in understanding the Kontsevich Invariant of a knot in the last decade or so. It appears that essential new ideas may be needed in ord …
14
votes
Accepted
Knot diagrams, sets of moves and equivalence relations
Very much so. There are a number of small industries centred around studying equivalence classes of knot diagrams generated by a set of moves.
The study of claspers. For example, $C_k$-moves are a sp …
82
votes
12
answers
15k
views
Compelling evidence that two basepoints are better than one
This question is inspired by an answer of Tim Porter.
Ronnie Brown pioneered a framework for homotopy theory in which one may consider multiple basepoints. These ideas are accessibly presented in his …
43
votes
8
answers
5k
views
What part of the fundamental group is captured by the second homology group?
Let $X$ be a connected CW complex. One can ask to what extent $H_\ast(X)$ determines $\pi_1(X)$. For example, it determines its abelianization, because the Hurewicz Theorem implies that $H_1(X)$ is is …
4
votes
Compelling evidence that two basepoints are better than one
The most convincing example I have found of "two basepoints being better than one" is the incorrect statement of the main result of the following paper:
Garoufalidis, Stavros, and Andrew Kricker. "A …
23
votes
6
answers
6k
views
Why chain homotopy when there is no topology in the background?
Given two morphisms between chain complexes $f_\bullet,g_\bullet\colon\,C_\bullet\longrightarrow D_\bullet$, a chain homotopy between them is a sequence of maps $\psi_n\colon\,C_n\longrightarrow D_{n …
22
votes
4
answers
2k
views
Natural setting for characteristic classes?
In my mind, algebraic topology is comprised of two components:
Chain complex information, which is intrinsic information concerning how your object may be built up out of simple "lego blocks".
Charac …
17
votes
Applications of arithmetic topology to number theory
Le and Murakami (HERE and HERE) discovered several previously unknown relations between multiple zeta values through the study of quantum invariants of knots. Further relations were later discovered t …
6
votes
Construction of invariants of 4-manifolds with the Kirby calculus
The Witten-Reshetikhin-Turaev approach to constructing quantum topological invariants of $3$-manifolds is to define them on framed links and to prove invariance under Kirby moves.
There is a paper of …
5
votes
Homological Algebra texts
Appendix 3 of Eisenbud's "Commutative Algebra" is the best short treatment I know. I find it fantastic. It clearly and concisely covers a surprising number of topics in homological algebra.
4
votes
Boundaries of smooth manifolds
This question was answered by Misha in a comment.
Nothing useful can be said about the handle decomposition of $N$, because, among other things, if an $n$-manifold $N$ has boundary $M$, then the conn …
13
votes
Accepted
What tools cannot work for orbifolds?
I'm not an expert and this might be wrong, but I think that Cerf theory should be impossible for orbifolds, and therefore all that comes from it, e.g. Kirby Calculus. Could somebody who knows please c …
8
votes
An "advanced beginner's" book on algebraic topology?
I think you're describing Spanier.
Everyone I know who has seriously studied from Spanier swears by it- it's an absolute classic. The approach is exactly as you describe- algebraic topology for grown …
17
votes
1
answer
610
views
Is there a notion of a chain complex with corners?
Roughly speaking, algebraic topology works by reducing questions about topological objects such as manifolds and cell to questions about chain complexes.
On the topological side, although in the PL …
4
votes
Accepted
Understanding four manifolds (more details inside)
My recommendation would be the book of Freedman and Quinn, Topology of 4-manifolds. It's hands-on, very very good, and suitable I think for a reader of your background. Indeed, I would strongly recom …