Five adjoints for constant presheaves on open sets
ID: five-adjoints-for-constant-presheaves-on-open-sets
For a nonempty topological space , the constant diagram functor on its open-set presheaf category lies in this five-term adjunction chain. The leftmost functor sends to the categorical presheaf equal to at the empty open set and empty elsewhere. The rightmost sends to the presheaf equal to at and a singleton elsewhere. A natural transformation from the former is determined by its empty-open component; a transformation into the latter is determined by its whole-space component. The middle adjunctions follow from restriction maps to the empty open set and from the whole space. Neither endpoint extends: the leftmost functor fails to preserve the terminal object, and the rightmost fails to preserve the initial object.
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