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Chris Schommer-Pries's user avatar
Chris Schommer-Pries's user avatar
Chris Schommer-Pries
  • Member for 15 years, 2 months
  • Last seen this week
  • Notre Dame, IN, United States
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Is any CW complex with only finitely many nonzero homology groups homotopic to a finite dimensional CW complex?
No, there is an $\pi_1$ issue. Let $G$ be an acyclic group, then the classifying space BG is a space whose homology vanishes, but it is not contractible and if G is infinite than it is not homotopy equivalent to a finite complex. An example of such an infinite acyclic group is the group G of all bijections of an infinite set.
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Does any non-Hausdorff manifold admit a metric tensor of signature $(p,q)$?
Taking the line with two origin's example further, as Thomas Rot points out the two different origins in that space are necessarily in any psuedo-metric open ball (centered at one of them say). They cannot be separated by open sets so the topology generated by the pseudo metric is not $T_0$. In particular the pseudometric topology is different from the topology as a non-Hausdorff manifold.
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Is Turaev-Viro-Barrett-Westbury stronger than homotopy?
As far as I know it is an open question whether Turaev-Viro tqfts can distinguish L(7,1) and L(7,2). I was just pointing out that the category that was expected to do this seems not to work.
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Understanding model independently the equivalence of two ways of obtaining homotopy types from categories
@DavidRoberts That is a fair point. I edited to use $Cat_{(\infty,0)}$.
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Topologies on compactly supported functions
More information and refs for topologies.
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Topologies on compactly supported functions
There is a variant of the notion of plot where you only require $\tilde{p}: M \times [0,1] \to \mathbb{R}$ to be continuous (but if you fix $t$, $p(t)$ is still smooth with compact support in the $x$-direction). I think what your argument really shows is that any $\tau_2$-continuous map $p: [0,1] \to C^\infty_c(\mathbb{R})$ has to be a plot of this kind.
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Topologies on compactly supported functions
@FanZheng This is regarding your potential counter-example to $\tau_2 \subseteq \tau_4$ two comments above. Your $p(t,x)$ does not define a plot. It is true that for each $t$ $p(t)$ is a compactly supported function, but the requirement to be a plot is that there is a single compact $K$ so that all the functions in the path are supported in $K$. As $t \to 0$ your $p(t)$ is supported on larger and larger subsets which contain at least $[-\frac{1}{t}, + \frac{1}{t}]$. Hence your $p(x,t)$ is not a plot and there is no counter example.
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Topologies on compactly supported functions
I will give a reference if I have time later today.
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