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Homotopy theory is an important sub-field of algebraic topology. It is mainly concerned with the properties and structures of spaces which are invariant under homotopy. Chief among these are the homotopy groups of spaces, specifically those of spheres. Homotopy theory includes a broad set of ideas and techniques, such as cohomology theories, spectra and stable homotopy theory, model categories, spectral sequences, and classifying spaces.

8 votes
0 answers
120 views

The homotopy inverse on Quillen's $S^{-1}S$ construction

Suppose $S$ is a symmetric monoidal groupoid. Take Quillen and Grayson's $S^{-1}S$-construction, which is a symmetric monoidal category with objects given by pairs $(m,n)$ and maps given by compositio …
Georg Lehner's user avatar
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5 votes
0 answers
212 views

Realizing the 0-th Postnikov truncation of a spectrum in the category of orthogonal/symmetri...

Suppose $E$ is a connective spectrum, then there exists a natural map in the stable homotopy category $\mathcal{SHC}$, $E \rightarrow P_0 E$, called the $0$-th Postnikov truncation, which is character …
Georg Lehner's user avatar
  • 2,303
1 vote

Commuting homotopy colimits and arbitrary products in spaces

I will answer my own question, in hope that it is helpful to someone. Given a functor $X:D \rightarrow Spc$ of $\infty$-categories, we can take the unstraightening of $X$ (the appropriate generalizati …
Georg Lehner's user avatar
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2 votes

Does Grayson/Quillen's "pre group completion" have a universal property?

It is the classifying category for the left action of $C$ on its product $C \times C$. Let me elaborate on this a bit further. Let $C$ be an $E_\infty$-monoid, for example represented by a symmetric m …
Georg Lehner's user avatar
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6 votes
1 answer
306 views

Commuting homotopy colimits and arbitrary products in spaces

Let $X : D \rightarrow Spc$ be a diagram with values in the $\infty$-category of spaces and $I$ some (discrete) set, not necessarily finite. ($D$ can be a 1-category if that makes statements easier, b …
Georg Lehner's user avatar
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