Relation of morphism properties with limits #
The following predicates are introduces for morphism properties P:
IsStableUnderBaseChange:Pis stable under base change if in all pullback squares, the left map satisfiesPif the right map satisfies it.IsStableUnderCobaseChange:Pis stable under cobase change if in all pushout squares, the right map satisfiesPif the left map satisfies it.
We define P.universally for the class of morphisms which satisfy P after any base change.
We also introduce properties IsStableUnderProductsOfShape, IsStableUnderLimitsOfShape,
IsStableUnderFiniteProducts, and similar properties for colimits and coproducts.
A morphism property is IsStableUnderBaseChange if the base change of such a morphism
still falls in the class.
- of_isPullback {X Y Y' S : C} {f : X ⟶ S} {g : Y ⟶ S} {f' : Y' ⟶ Y} {g' : Y' ⟶ X} (sq : CategoryTheory.IsPullback f' g' g f) (hg : P g) : P g'
Instances
A morphism property is IsStableUnderCobaseChange if the cobase change of such a morphism
still falls in the class.
- of_isPushout {A A' B B' : C} {f : A ⟶ A'} {g : A ⟶ B} {f' : B ⟶ B'} {g' : A' ⟶ B'} (sq : CategoryTheory.IsPushout g f f' g') (hf : P f) : P f'
Instances
Alternative constructor for IsStableUnderBaseChange.
An alternative constructor for IsStableUnderCobaseChange.
The property that a morphism property W is stable under limits
indexed by a category J.
Equations
- One or more equations did not get rendered due to their size.
Instances For
The property that a morphism property W is stable under colimits
indexed by a category J.
Equations
- One or more equations did not get rendered due to their size.
Instances For
The property that a morphism property W is stable under products indexed by a type J.
Equations
- W.IsStableUnderProductsOfShape J = W.IsStableUnderLimitsOfShape (CategoryTheory.Discrete J)
Instances For
The property that a morphism property W is stable under coproducts indexed by a type J.
Equations
- W.IsStableUnderCoproductsOfShape J = W.IsStableUnderColimitsOfShape (CategoryTheory.Discrete J)
Instances For
The condition that a property of morphisms is stable by finite products.
Instances
The condition that a property of morphisms is stable by finite coproducts.
Instances
For P : MorphismProperty C, P.diagonal is a morphism property that holds for f : X ⟶ Y
whenever P holds for X ⟶ Y xₓ Y.
Equations
- P.diagonal f = P (CategoryTheory.Limits.pullback.diagonal f)
Instances For
If P is multiplicative and stable under base change, having the of-postcomp property
wrt. Q is equivalent to Q implying P on the diagonal.
P.universally holds for a morphism f : X ⟶ Y iff P holds for all X ×[Y] Y' ⟶ Y'.
Equations
- P.universally f = ∀ ⦃X' Y' : C⦄ (i₁ : X' ⟶ X) (i₂ : Y' ⟶ Y) (f' : X' ⟶ Y'), CategoryTheory.IsPullback f' i₁ i₂ f → P f'