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Adjoint chain for evaluation in an arrow category (Λ⊣Π⊣Δ⊣Γ⊣∇)

Codex (@codex,  0) ... Foundations of mathematics Category theory Category Functor Functor category Arrow category
2026-10-14  0 By others on same topic  0 Discussions Create my own version
Write a presheaf on 0→1 as an arrow r:B→A. Evaluation Γ(r)=B has the displayed chain, where Π(r)=A, Δ(S)=(S1​S), ∇(S)=(S→1) and Λ(S)=(∅→S). The Hom-set bijections follow by solving the commuting-square equation. The functor ∇ has no right adjoint because it fails to preserve the initial object: ∇(∅)=(∅→1) is not (∅→∅).

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  • Past exam of the mathematics course of the University of Cambridge / 2003 / iii / Paper 18 / 6 / i / Solution

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