Rejective full subcategories and equivalence transport #
Rejectivity itself is purely categorical. No zero object, additive structure, kernels, cokernels, or module structure enters its definition or its invariance under equivalence.
A full subcategory is right rejective when its inclusion has a right adjoint with componentwise monic counit.
- coreflector : CategoryTheory.Functor C P.FullSubcategory
- adjunction : P.ι ⊣ self.coreflector
- counit_mono (X : C) : CategoryTheory.Mono (self.adjunction.counit.app X)
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Propositional form of categorical right rejectivity.
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A full subcategory is left rejective when its inclusion has a left adjoint with componentwise epic unit.
- reflector : CategoryTheory.Functor C P.FullSubcategory
- adjunction : self.reflector ⊣ P.ι
- unit_epi (X : C) : CategoryTheory.Epi (self.adjunction.unit.app X)
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Propositional form of categorical left rejectivity.
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The replete image predicate on the target of an equivalence, expressed as pullback along its chosen inverse.
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Restriction of the inverse equivalence functor to the pulled-back object property.
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Restriction of the forward equivalence functor. Repleteness of P
supplies membership after applying the unit isomorphism.
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The unit of the ambient equivalence restricted to the full subcategories.
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The counit of the ambient equivalence restricted to the full subcategories.
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The equivalence induced on a replete full subcategory.
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The composite of the transported source inclusion with the ambient equivalence is canonically the target inclusion.
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The transported right adjoint.
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The composite adjunction, with its left adjoint normalized back to the literal inclusion of the transported full subcategory.
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The transported left adjoint.
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The composite left-rejective adjunction, with its right adjoint normalized to the target inclusion.
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The transported counit is monic. The proof separates the two composed adjunctions and the final normalization isomorphism, so typeclass search only sees composites of mapped monomorphisms and isomorphisms.
The transported unit is epic, by the dual componentwise argument.
Right rejective data transports along a categorical equivalence.
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Left rejective data transports along a categorical equivalence.
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Right rejectivity transports in the forward direction.
Left rejectivity transports in the forward direction.
Pulling the image predicate back through the inverse equivalence recovers the original predicate. Repleteness is the only input.
Right rejectivity is invariant under categorical equivalence.
Left rejectivity is invariant under categorical equivalence.