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In category theory, a branch of mathematics, the cocyle category of objects X, Y in a model category is a category in which the objects are pairs of maps $X{\overset {f}{\leftarrow }}Z{\overset {g}{\rightarrow }}Y$ and the morphisms are obvious commutative diagrams between them. It is denoted by $H(X,Y)$. (It may also be defined using the language of 2-category.)

One has: if the model category is right proper and is such that weak equivalences are closed under finite products,

$\pi _{0}H(X,Y)\to [X,Y],\quad (f,g)\mapsto g\circ f^{-1}$

is bijective.

References

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