Calculus of fractions #
Following the definitions by [Gabriel and Zisman][gabriel-zisman-1967],
given a morphism property W : MorphismProperty C
on a category C
,
we introduce the class W.HasLeftCalculusOfFractions
. The main
result (TODO) is that if L : C ⥤ D
is a localization functor for W
,
then for any morphism L.obj X ⟶ L.obj Y
in D
, there exists an auxiliary
object Y' : C
and morphisms g : X ⟶ Y'
and s : Y ⟶ Y'
, with W s
, such
that the given morphism is a sort of fraction g / s
, or more precisely of
the form L.map g ≫ (Localization.isoOfHom L W s hs).inv
.
References #
- [P. Gabriel, M. Zisman, Calculus of fractions and homotopy theory][gabriel-zisman-1967]
A left fraction from X : C
to Y : C
for W : MorphismProperty C
consists of the
datum of an object Y' : C
and maps f : X ⟶ Y'
and s : Y ⟶ Y'
such that W s
.
- Y' : C
the auxiliary object of a left fraction
- f : X ⟶ self.Y'
the numerator of a left fraction
- s : Y ⟶ self.Y'
the denominator of a left fraction
- hs : W self.s
the condition that the denominator belongs to the given morphism property
Instances For
The left fraction from X
to Y
given by a morphism f : X ⟶ Y
.
Equations
Instances For
The left fraction from X
to Y
given by a morphism s : Y ⟶ X
such that W s
.
Equations
Instances For
If φ : W.LeftFraction X Y
and L
is a functor which inverts W
, this is the
induced morphism L.obj X ⟶ L.obj Y
Equations
- One or more equations did not get rendered due to their size.
Instances For
A right fraction from X : C
to Y : C
for W : MorphismProperty C
consists of the
datum of an object X' : C
and maps s : X' ⟶ X
and f : X' ⟶ Y
such that W s
.
- X' : C
the auxiliary object of a right fraction
- s : self.X' ⟶ X
the denominator of a right fraction
- hs : W self.s
the condition that the denominator belongs to the given morphism property
- f : self.X' ⟶ Y
the numerator of a right fraction
Instances For
The right fraction from X
to Y
given by a morphism f : X ⟶ Y
.
Equations
Instances For
The right fraction from X
to Y
given by a morphism s : Y ⟶ X
such that W s
.
Equations
Instances For
If φ : W.RightFraction X Y
and L
is a functor which inverts W
, this is the
induced morphism L.obj X ⟶ L.obj Y
Equations
- One or more equations did not get rendered due to their size.
Instances For
A multiplicative morphism property W
has left calculus of fractions if
any right fraction can be turned into a left fraction and that two morphisms
that can be equalized by precomposition with a morphism in W
can also
be equalized by postcomposition with a morphism in W
.
- id_mem' : ∀ (X : C), W (CategoryTheory.CategoryStruct.id X)
- stableUnderComposition : CategoryTheory.MorphismProperty.StableUnderComposition W
- exists_leftFraction : ∀ ⦃X Y : C⦄ (φ : CategoryTheory.MorphismProperty.RightFraction W X Y), ∃ (ψ : CategoryTheory.MorphismProperty.LeftFraction W X Y), CategoryTheory.CategoryStruct.comp φ.f ψ.s = CategoryTheory.CategoryStruct.comp φ.s ψ.f
- ext : ∀ ⦃X' X Y : C⦄ (f₁ f₂ : X ⟶ Y) (s : X' ⟶ X), W s → CategoryTheory.CategoryStruct.comp s f₁ = CategoryTheory.CategoryStruct.comp s f₂ → ∃ (Y' : C) (t : Y ⟶ Y') (_ : W t), CategoryTheory.CategoryStruct.comp f₁ t = CategoryTheory.CategoryStruct.comp f₂ t
Instances
A multiplicative morphism property W
has right calculus of fractions if
any left fraction can be turned into a right fraction and that two morphisms
that can be equalized by postcomposition with a morphism in W
can also
be equalized by precomposition with a morphism in W
.
- id_mem' : ∀ (X : C), W (CategoryTheory.CategoryStruct.id X)
- stableUnderComposition : CategoryTheory.MorphismProperty.StableUnderComposition W
- exists_rightFraction : ∀ ⦃X Y : C⦄ (φ : CategoryTheory.MorphismProperty.LeftFraction W X Y), ∃ (ψ : CategoryTheory.MorphismProperty.RightFraction W X Y), CategoryTheory.CategoryStruct.comp ψ.s φ.f = CategoryTheory.CategoryStruct.comp ψ.f φ.s
- ext : ∀ ⦃X Y Y' : C⦄ (f₁ f₂ : X ⟶ Y) (s : Y ⟶ Y'), W s → CategoryTheory.CategoryStruct.comp f₁ s = CategoryTheory.CategoryStruct.comp f₂ s → ∃ (X' : C) (t : X' ⟶ X) (_ : W t), CategoryTheory.CategoryStruct.comp t f₁ = CategoryTheory.CategoryStruct.comp t f₂
Instances
A choice of a left fraction deduced from a right fraction for a morphism property W
when W
has left calculus of fractions.
Equations
- One or more equations did not get rendered due to their size.
Instances For
A choice of a right fraction deduced from a left fraction for a morphism property W
when W
has right calculus of fractions.
Equations
- One or more equations did not get rendered due to their size.
Instances For
The equivalence relation on left fractions for a morphism property W
.
Equations
- One or more equations did not get rendered due to their size.
Instances For
Auxiliary definition for the composition of left fractions.
Equations
- One or more equations did not get rendered due to their size.
Instances For
The equivalence class of z₁.comp₀ z₂ z₃
does not depend on the choice of z₃
provided
they satisfy the compatibility z₂.f ≫ z₃.s = z₁.s ≫ z₃.f
.
The morphisms in the constructed localized category for a morphism property W
that has left calculus of fractions are equivalence classes of left fractions.
Equations
- CategoryTheory.MorphismProperty.LeftFraction.Localization.Hom W X Y = Quot CategoryTheory.MorphismProperty.LeftFractionRel
Instances For
The morphism in the constructed localized category that is induced by a left fraction.
Equations
- CategoryTheory.MorphismProperty.LeftFraction.Localization.Hom.mk z = Quot.mk CategoryTheory.MorphismProperty.LeftFractionRel z
Instances For
Auxiliary definition towards the definition of the composition of morphisms in the constructed localized category for a morphism property that has left calculus of fractions.
Equations
- One or more equations did not get rendered due to their size.
Instances For
Composition of morphisms in the constructed localized category for a morphism property that has left calculus of fractions.
Equations
- One or more equations did not get rendered due to their size.
Instances For
The constructed localized category for a morphism property that has left calculus of fractions.
Instances For
Equations
- CategoryTheory.MorphismProperty.LeftFraction.Localization.instCategoryLocalization = CategoryTheory.Category.mk
The localization functor to the constructed localized category for a morphism property that has left calculus of fractions.
Equations
- One or more equations did not get rendered due to their size.