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Continuum theory, point-set topology, spaces with algebraic structure, foundations, dimension theory, local and global properties.

22 votes
0 answers
668 views

Are there "chain complexes" and "homology groups" taking values in pairs of topological spaces?

Throughout this question, notation of the form $(X,A)$ denotes a sufficiently nice pair of topological spaces. I think for most of what I'm saying here, it is enough to assume that the inclusion $A \h …
Vidit Nanda's user avatar
  • 15.5k
8 votes
1 answer
766 views

What information can one recover from the induced map on homology?

The following question came up while constructing delay embeddings of time series data. Consider an unknown topological space $X$ and an unknown continuous function $f:X \to X$. We are given a combin …
Vidit Nanda's user avatar
  • 15.5k
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
  • 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
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
3 votes
Accepted

A Fixed point Theorem that does not need the convexity of set valued map?

In the absence of convex images, one typically relies on algebraic topology as you have guessed. If your set-valued map has a reasonably nice domain and contractible images, then you can easily string …
Vidit Nanda's user avatar
  • 15.5k
3 votes
1 answer
148 views

Metric on the set of Polyhedral Decompositions of a Compact Metric Space

Let $(X,d)$ be a compact metric space of finite diameter. Recall that we can always compute the Hausdorff distance between subsets $A, B \subset X$ via $$ d_H(A,B) = \max\left[\sup_{a\in A}\inf_{b\in …
Vidit Nanda's user avatar
  • 15.5k