KnowraHairy ball theoremLinked fromLinked fromThe 3 pages that link to Hairy ball theorem, each with the reason it gives.All 3Broader topic 2Related 1Differential topologyRelated: It links the existence of smooth vector fields to a sphere's topological structure.Poincaré–Hopf theoremBroader topic: The sphere’s nonzero Euler characteristic forces a zero by Poincaré–Hopf.Characteristic classBroader topic: The Euler class explains the obstruction to a nowhere-vanishing tangent field.