homotopy theory, (∞,1)-category theory, homotopy type theory
flavors: stable, equivariant, rational, p-adic, proper, geometric, cohesive, directed…
models: topological, simplicial, localic, …
see also algebraic topology
Introductions
Definitions
Paths and cylinders
Homotopy groups
Basic facts
Theorems
A homotopy sphere is a topological space which need not be homeomorphic to an n-sphere, but which has the same homotopy type as an -sphere.
Every homotopy sphere is a rational homotopy sphere.
Every homotopy sphere is a homology sphere.
Every simply connected homology sphere is a homotopy sphere.
A path-connected, -connected, orientable and closed -manifold is a homotopy--sphere.
A path-connected, -connected, orientable and closed -manifold is a homotopy--sphere.
Every smooth manifold homotopy-4-sphere is homeomorphic to the actual 4-sphere.
(due to Michael Freedman, see Siebenmann 1982)
Laurent Siebenmann: La conjecture de Poincaré topologique en dimension 4, Séminaire Bourbaki : volume 1981/82, exposés 579-596, Astérisque, no. 92-93 (1982), Talk no. 588 [numdam:SB_1981-1982__24__219_0]
Laurent Siebenmann (translation by M. H. Kim & M. Powell): Topological Poincaré conjecture in dimension 4 (the work of M. H. Freedman), Celebratio Mathematica [webpage]
Last revised on April 15, 2025 at 16:43:49. See the history of this page for a list of all contributions to it.