rational homology sphere in nLab

n-sphere

• unit sphere, polar coordinates

• round sphere, squashed sphere

• hemisphere, equator

• stereographic projection

• homotopy groups of spheres

• homotopy sphere, rational homotopy sphere, Cohomotopy

• spherical fibration, twisted Cohomotopy

• sphere spectrum, stable Cohomotopy theory

• homology sphere

• rational homotopy sphere, rational n-sphere

• motivic sphere

• group actions on spheres

• representation sphere, equivariant Cohomotopy

• Reeb sphere theorem

• sphere packing

• Music of the Spheres

low dimensional n-spheres

• circle

  • real projective spaceℝP 1\,\mathbb{R}P^1

• 2-sphere

  • complex projective lineℂP 1\,\mathbb{C}P^1: Riemann sphere

  • geometric quantization of the 2-sphere

  • fuzzy 2-sphere

• 3-sphere

  • fuzzy 3-sphere

• 4-sphere

  • quaternionic projective lineℍP 1\,\mathbb{H}P^1

  • fuzzy 4-sphere

• 5-sphere

• 6-sphere

• 7-sphere

  • exotic 7-sphere

• 8-sphere

  • octonionic projective line𝕆P 1\,\mathbb{O}P^1

• 13-sphere

• 15-sphere

• infinite-dimensional sphere

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

• Introduction to Basic Homotopy Theory

• Introduction to Abstract Homotopy Theory

• geometry of physics – homotopy types

Definitions

• homotopy, higher homotopy

• homotopy type

• Pi-algebra, spherical object and Pi(A)-algebra

• homotopy coherent category theory

  • homotopical category

    • model category

    • category of fibrant objects, cofibration category

    • Waldhausen category

  • homotopy category

    • Ho(Top)

• (∞,1)-category

  • homotopy category of an (∞,1)-category

Paths and cylinders

• left homotopy

  • cylinder object

  • mapping cone

• right homotopy

  • path object

  • mapping cocone

  • universal bundle

• interval object

  • homotopy localization

  • infinitesimal interval object

Homotopy groups

• homotopy group

  • fundamental group

    • fundamental group of a topos

  • Brown-Grossman homotopy group

  • categorical homotopy groups in an (∞,1)-topos

  • geometric homotopy groups in an (∞,1)-topos

• fundamental ∞-groupoid

  • fundamental groupoid

    • path groupoid

  • fundamental ∞-groupoid in a locally ∞-connected (∞,1)-topos

  • fundamental ∞-groupoid of a locally ∞-connected (∞,1)-topos

• fundamental (∞,1)-category

  • fundamental category

Basic facts

• fundamental group of the circle is the integers

Theorems

• fundamental theorem of covering spaces

• Freudenthal suspension theorem

• Blakers-Massey theorem

• higher homotopy van Kampen theorem

• nerve theorem

• Whitehead's theorem

• Hurewicz theorem

• Galois theory

• homotopy hypothesis-theorem