Dinatural transformation

In category theory, a dinatural transformation \alpha between two functors

S,T�: \mathrm{C}^{\mathrm{op}}\times\mathrm{C}\to\mathrm{X},

written

\alpha�: S\ddot\to T,

is a function which to every object c of C associates an arrow

\alpha_c�: S(c,c)\to T(c,c) of X

and satisfies the following coherence property: for every morphism f:c\to c' of C the diagram

commutes.

The composition of two dinatural transformations need not be dinatural.

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