Adjoint chain for the objects of a category
ID: adjoint-chain-for-the-objects-of-a-category
For small categories, the object functor has left adjoint the discrete category functor and right adjoint the indiscrete category functor. Connected components, defined by zigzags of morphisms, give a left adjoint to the discrete functor. There is no further left adjoint: fails the equalizer of two functors selecting distinct objects of the indiscrete two-object category. There is no further right adjoint: the indiscrete functor fails the coproduct of two singleton sets.
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