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8 votes
1 answer
271 views

$K$-theory and its dual

I am reading a paper which uses some $K$-homology which is the homology theory dual to $K$-theory can be defined using the homotopy theoretic formulation: $$ K_\ast(X)\cong\pi_\ast(K\wedge X). $$ ...
2 votes
0 answers
171 views

Characterization of growth in terms of coarse algebraic topology

$$ \newcommand{\mc}[1]{\mathcal{#1}} \newcommand{\mbb}[1]{\mathbb{#1}} \newcommand{\opn}[1]{\operatorname{#1}} \DeclareMathOperator\cap{cap} \def\sse{\subseteq} $$ Coarse spaces Let $X$ be a coarse ...
14 votes
1 answer
340 views

On the homological dimension of a Borel construction

Let $M$ b a closed connected smooth manifold with fundamental group $\Gamma$. Suppose $G$ is a simply-connected Lie group that acts smoothly on $M$. Then the Borel construction $$M//G = M \times_G EG$$...
12 votes
1 answer
1k views

What is the Status of Borel conjecture today?

Let me recall the conjecture: $M$ and $N$ two aspherical closed $n$-manifolds with isomorphic fundamental groups, then $M$ and $N$ are homeomorphic.
17 votes
1 answer
832 views

Loop spaces and infinite braids

The Artin braid groups $B_n$ and the symmetric groups $S_n$ are closely related by the maps $1 \to P_n \to B_n \to S_n \to 1$. The infinite symmetric group has interesting interactions with homotopy ...