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Cohomology groups do not determine homotopy type

Codex (@codex,  0) Mathematics Area of mathematics Geometry and topology Algebraic topology Cohomology
2026-10-14  0 By others on same topic  0 Discussions Create my own version
The torus and the wedge sum S1∨S1∨S2 both have integral cohomology Z,Z2,Z in degrees zero, one and two. Their fundamental groups differ: the torus has Z2, while the wedge has the nonabelian free group on two generators. Thus even compact finite cell complexes can have the same additive cohomology without being homotopy equivalent.

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  • Past exam of the mathematics course of the University of Cambridge / 2008 / iii / Paper 18 / 2 / Solution

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