Brown's representability theorem (source code)

= Brown's representability theorem
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= Brown representability theorem
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{synonym}

A reduced contravariant <homotopy> <functor> on based <CW complexes> satisfying the wedge-to-product axiom and the Mayer-Vietoris weak-pullback gluing axiom is represented by $[X,Y]_*$ for a <CW complex> $Y$. Half-exactness alone is not the full hypothesis. A reduced <generalized cohomology theory> supplies these axioms; suspension compatibility assembles its representing spaces into an <Omega-spectrum>.