Cihan
  • Member for 9 years, 11 months
  • Last seen this week
Is every open topological $d$-manifold homotopy equivalent to a CW-complex of dimension $\leq d-1$?
Accepted answer
6 votes

$\DeclareMathOperator{\co}{H}$ $\DeclareMathOperator{\ch}{C}$ $\newcommand{\zz}{\mathbb{Z}}$ $\newcommand{\nn}{\mathbb{N}}$ $\newcommand{\A}{\mathcal{A}}$ $\newcommand{\B}{\mathcal{B}}$ $\...

View answer
Non-existence of projective covers
Accepted answer
6 votes

The mod-2 reduction is a functor from $\mathbb{Z}G$-modules to $\mathbb{F}_2G$-modules that preserves direct sums , because for instance it can be realized as tensoring with $\mathbb{F}_2$. Also if $M$...

View answer
What do absolute neighborhood retracts look like?
4 votes

I find Cauty's result a good crutch to think about ANRs: A metrizable space is an ANR if and only if every open subset has the homotopy type of a CW complex.

View answer
Equivariant Mobius inversion
2 votes

This is more of a long comment. I am not sure I understand your construction, but the sort of alternating sum you take has a preimage in the Burnside ring, and is often called the "Lefschetz invariant"...

View answer