HepLean Documentation

Mathlib.CategoryTheory.MorphismProperty.Basic

Properties of morphisms #

We provide the basic framework for talking about properties of morphisms. The following meta-property is defined

A MorphismProperty C is a class of morphisms between objects in C.

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    theorem CategoryTheory.MorphismProperty.ext {C : Type u} [CategoryTheory.Category.{v, u} C] (W W' : CategoryTheory.MorphismProperty C) (h : ∀ ⦃X Y : C⦄ (f : X Y), W f W' f) :
    W = W'

    The morphism property in Cᵒᵖ associated to a morphism property in C

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    • P.op f = P f.unop
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      The morphism property in C associated to a morphism property in Cᵒᵖ

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      • P.unop f = P f.op
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        The inverse image of a MorphismProperty D by a functor C ⥤ D

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        • P.inverseImage F f = P (F.map f)
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          The image (up to isomorphisms) of a MorphismProperty C by a functor C ⥤ D

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            A morphism property P satisfies P.RespectsRight Q if it is stable under post-composition with morphisms satisfying Q, i.e. whenever P holds for f and Q holds for i then P holds for f ≫ i.

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              A morphism property P satisfies P.RespectsLeft Q if it is stable under pre-composition with morphisms satisfying Q, i.e. whenever P holds for f and Q holds for i then P holds for i ≫ f.

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                class CategoryTheory.MorphismProperty.Respects {C : Type u} [CategoryTheory.Category.{v, u} C] (P Q : CategoryTheory.MorphismProperty C) extends P.RespectsLeft Q, P.RespectsRight Q :

                A morphism property P satisfies P.Respects Q if it is stable under composition on the left and right by morphisms satisfying Q.

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                  instance CategoryTheory.MorphismProperty.RespectsLeft.inf {C : Type u} [CategoryTheory.Category.{v, u} C] (P₁ P₂ Q : CategoryTheory.MorphismProperty C) [P₁.RespectsLeft Q] [P₂.RespectsLeft Q] :
                  (P₁ P₂).RespectsLeft Q
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                  instance CategoryTheory.MorphismProperty.RespectsRight.inf {C : Type u} [CategoryTheory.Category.{v, u} C] (P₁ P₂ Q : CategoryTheory.MorphismProperty C) [P₁.RespectsRight Q] [P₂.RespectsRight Q] :
                  (P₁ P₂).RespectsRight Q
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                  @[reducible, inline]

                  P respects isomorphisms, if it respects the morphism property isomorphisms C, i.e. it is stable under pre- and postcomposition with isomorphisms.

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                    theorem CategoryTheory.MorphismProperty.RespectsIso.mk {C : Type u} [CategoryTheory.Category.{v, u} C] (P : CategoryTheory.MorphismProperty C) (hprecomp : ∀ {X Y Z : C} (e : X Y) (f : Y Z), P fP (CategoryTheory.CategoryStruct.comp e.hom f)) (hpostcomp : ∀ {X Y Z : C} (e : Y Z) (f : X Y), P fP (CategoryTheory.CategoryStruct.comp f e.hom)) :
                    P.RespectsIso
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                    The closure by isomorphisms of a MorphismProperty

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                      theorem CategoryTheory.MorphismProperty.monotone_isoClosure {C : Type u} [CategoryTheory.Category.{v, u} C] :
                      Monotone CategoryTheory.MorphismProperty.isoClosure
                      @[deprecated CategoryTheory.MorphismProperty.cancel_left_of_respectsIso]

                      Alias of CategoryTheory.MorphismProperty.cancel_left_of_respectsIso.

                      @[deprecated CategoryTheory.MorphismProperty.cancel_right_of_respectsIso]

                      Alias of CategoryTheory.MorphismProperty.cancel_right_of_respectsIso.

                      @[deprecated CategoryTheory.MorphismProperty.arrow_iso_iff]

                      Alias of CategoryTheory.MorphismProperty.arrow_iso_iff.

                      @[deprecated CategoryTheory.MorphismProperty.arrow_mk_iso_iff]

                      Alias of CategoryTheory.MorphismProperty.arrow_mk_iso_iff.

                      @[deprecated CategoryTheory.MorphismProperty.isoClosure_eq_self]

                      Alias of CategoryTheory.MorphismProperty.isoClosure_eq_self.

                      If W₁ and W₂ are morphism properties on two categories C₁ and C₂, this is the induced morphism property on C₁ × C₂.

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                      • W₁.prod W₂ f = (W₁ f.1 W₂ f.2)
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                        def CategoryTheory.MorphismProperty.pi {J : Type w} {C : JType u} [(j : J) → CategoryTheory.Category.{v, u} (C j)] (W : (j : J) → CategoryTheory.MorphismProperty (C j)) :

                        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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                          The morphism property on J ⥤ C which is defined objectwise from W : MorphismProperty C.

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                          • W.functorCategory J f = ∀ (j : J), W (f.app j)
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                            Given W : MorphismProperty C, this is the morphism property on Arrow C of morphisms whose left and right parts are in W.

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                            • W.arrow f = (W f.left W f.right)
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