Properties of morphisms #
We provide the basic framework for talking about properties of morphisms. The following meta-properties are defined
RespectsIso:Prespects isomorphisms ifP f → P (e ≫ f)andP f → P (f ≫ e), whereeis an isomorphism.StableUnderComposition:Pis stable under composition ifP f → P g → P (f ≫ g).StableUnderBaseChange:Pis stable under base change if in all pullback squares, the left map satisfiesPif the right map satisfies it.StableUnderCobaseChange:Pis stable under cobase change if in all pushout squares, the right map satisfiesPif the left map satisfies it.
A MorphismProperty C is a class of morphisms between objects in C.
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- CategoryTheory.MorphismProperty C = (⦃X Y : C⦄ → (X ⟶ Y) → Prop)
Instances For
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- CategoryTheory.instCompleteLatticeMorphismProperty C = id inferInstance
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- CategoryTheory.instInhabitedMorphismProperty C = { default := ⊤ }
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- CategoryTheory.MorphismProperty.instHasSubsetMorphismProperty = { Subset := fun (P₁ P₂ : CategoryTheory.MorphismProperty C) => ∀ ⦃X Y : C⦄ (f : X ⟶ Y), P₁ f → P₂ f }
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- CategoryTheory.MorphismProperty.instInterMorphismProperty = { inter := fun (P₁ P₂ : CategoryTheory.MorphismProperty C) (x x_1 : C) (f : x ⟶ x_1) => P₁ f ∧ P₂ f }
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The morphism property in Cᵒᵖ associated to a morphism property in C
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- CategoryTheory.MorphismProperty.op P f = P f.unop
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The morphism property in C associated to a morphism property in Cᵒᵖ
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- CategoryTheory.MorphismProperty.unop P f = P f.op
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The inverse image of a MorphismProperty D by a functor C ⥤ D
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- CategoryTheory.MorphismProperty.inverseImage P F f = P (F.toPrefunctor.map f)
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The image (up to isomorphisms) of a MorphismProperty C by a functor C ⥤ D
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- CategoryTheory.MorphismProperty.map P F f = ∃ (X' : C) (Y' : C) (f' : X' ⟶ Y') (_ : P f'), Nonempty (CategoryTheory.Arrow.mk (F.toPrefunctor.map f') ≅ CategoryTheory.Arrow.mk f)
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A morphism property RespectsIso if it still holds when composed with an isomorphism
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The closure by isomorphisms of a MorphismProperty
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- CategoryTheory.MorphismProperty.isoClosure P f = ∃ (Y₁ : C) (Y₂ : C) (f' : Y₁ ⟶ Y₂) (_ : P f'), Nonempty (CategoryTheory.Arrow.mk f' ≅ CategoryTheory.Arrow.mk f)
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A morphism property is StableUnderComposition if the composition of two such morphisms
still falls in the class.
Equations
- CategoryTheory.MorphismProperty.StableUnderComposition P = ∀ ⦃X Y Z : C⦄ (f : X ⟶ Y) (g : Y ⟶ Z), P f → P g → P (CategoryTheory.CategoryStruct.comp f g)
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A morphism property is StableUnderInverse if the inverse of a morphism satisfying
the property still falls in the class.
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- CategoryTheory.MorphismProperty.StableUnderInverse P = ∀ ⦃X Y : C⦄ (e : X ≅ Y), P e.hom → P e.inv
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A morphism property is StableUnderBaseChange if the base change of such a morphism
still falls in the class.
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- CategoryTheory.MorphismProperty.StableUnderBaseChange P = ∀ ⦃X Y Y' S : C⦄ ⦃f : X ⟶ S⦄ ⦃g : Y ⟶ S⦄ ⦃f' : Y' ⟶ Y⦄ ⦃g' : Y' ⟶ X⦄, CategoryTheory.IsPullback f' g' g f → P g → P g'
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A morphism property is StableUnderCobaseChange if the cobase change of such a morphism
still falls in the class.
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- CategoryTheory.MorphismProperty.StableUnderCobaseChange P = ∀ ⦃A A' B B' : C⦄ ⦃f : A ⟶ A'⦄ ⦃g : A ⟶ B⦄ ⦃f' : B ⟶ B'⦄ ⦃g' : A' ⟶ B'⦄, CategoryTheory.IsPushout g f f' g' → P f → P f'
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If P : MorphismProperty C and F : C ⥤ D, then
P.IsInvertedBy F means that all morphisms in P are mapped by F
to isomorphisms in D.
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- CategoryTheory.MorphismProperty.IsInvertedBy P F = ∀ ⦃X Y : C⦄ (f : X ⟶ Y), P f → CategoryTheory.IsIso (F.toPrefunctor.map f)
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Given app : Π X, F₁.obj X ⟶ F₂.obj X where F₁ and F₂ are two functors,
this is the morphism_property C satisfied by the morphisms in C with respect
to whom app is natural.
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The MorphismProperty C satisfied by isomorphisms in C.
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The MorphismProperty C satisfied by monomorphisms in C.
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The MorphismProperty C satisfied by epimorphisms in C.
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The full subcategory of C ⥤ D consisting of functors inverting morphisms in W
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A constructor for W.FunctorsInverting D
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- CategoryTheory.MorphismProperty.FunctorsInverting.mk F hF = { obj := F, property := hF }
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For P : MorphismProperty C, P.diagonal is a morphism property that holds for f : X ⟶ Y
whenever P holds for X ⟶ Y xₓ Y.
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P.universally holds for a morphism f : X ⟶ Y iff P holds for all X ×[Y] Y' ⟶ Y'.
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- CategoryTheory.MorphismProperty.universally P f = ∀ ⦃X' Y' : C⦄ (i₁ : X' ⟶ X) (i₂ : Y' ⟶ Y) (f' : X' ⟶ Y'), CategoryTheory.IsPullback f' i₁ i₂ f → P f'
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Injectiveness (in a concrete category) as a MorphismProperty
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Surjectiveness (in a concrete category) as a MorphismProperty
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Bijectiveness (in a concrete category) as a MorphismProperty
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Typeclass expressing that a morphism property contain identities.
- id_mem' : ∀ (X : C), W (CategoryTheory.CategoryStruct.id X)
for all
X : C, the identity ofXsatisfies the morphism property
Instances
A morphism property is multiplicative if it contains identities and is stable by composition.
- id_mem' : ∀ (X : C), W (CategoryTheory.CategoryStruct.id X)
- stableUnderComposition : CategoryTheory.MorphismProperty.StableUnderComposition W
compatibility of
Instances
If W₁ and W₂ are morphism properties on two categories C₁ and C₂,
this is the induced morphism property on C₁ × C₂.
Equations
- CategoryTheory.MorphismProperty.prod W₁ W₂ f = (W₁ f.1 ∧ W₂ f.2)
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If W j are morphism properties on categories C j for all j, this is the
induced morphism property on the category ∀ j, C j.
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- CategoryTheory.MorphismProperty.pi W f = ∀ (j : J), W j (f j)
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The morphism property on J ⥤ C which is defined objectwise
from W : MorphismProperty C.
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- CategoryTheory.MorphismProperty.functorCategory W J f = ∀ (j : J), W (f.app j)
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The property that a morphism property W is stable under limits
indexed by a category J.
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The property that a morphism property W is stable under products indexed by a type J.
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The condition that a property of morphisms is stable by finite products.
- isStableUnderProductsOfShape : ∀ (J : Type) [inst : Finite J], CategoryTheory.MorphismProperty.IsStableUnderProductsOfShape W J