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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
1 answer
398 views

Reduction of structure group and classifying spaces

Let $H, G$ be topological groups and $\phi : H \to G$ a group homomorphism. Let $M$ be a paracompact topological space. For any principal $G$-bundle $P \to M$, a reduction (or sometimes 'lift') of its …
Arnav Das's user avatar
  • 113
4 votes
1 answer
269 views

Do the two orientations on an orientable manifold $M$ uniquely witness lifts of $\tau_M: M \...

For an orientable $n$-manifold $M$ and its (orthonormal) frame bundle classifying map $\tau_M : M \to BO(n)$, we have a lift diagram of the following sort: There are two orientations on $M$. Is it ev …
Arnav Das's user avatar
  • 113
3 votes
2 answers
338 views

Is this true of the frame bundle $\operatorname{Fr}(M)$?

On an orientable (Riemannian) $n$-manifold $M$, with orthonormal frame bundle $\operatorname{Fr}(M)$, we have that the tangent bundle classifying map $\tau_M : M \to B{\operatorname O(n)}$ lifts to $B …
Arnav Das's user avatar
  • 113