Properties of morphisms between Schemes #
We provide the basic framework for talking about properties of morphisms between Schemes.
A MorphismProperty Scheme is a predicate on morphisms between schemes, and an
AffineTargetMorphismProperty is a predicate on morphisms into affine schemes. Given a
P : AffineTargetMorphismProperty, we may construct a MorphismProperty called
targetAffineLocally P that holds for f : X ⟶ Y whenever P holds for the
restriction of f on every affine open subset of Y.
Main definitions #
AlgebraicGeometry.AffineTargetMorphismProperty.IsLocal: We say thatP.IsLocalifPsatisfies the assumptions of the affine communication lemma (AlgebraicGeometry.of_affine_open_cover). That is,
Prespects isomorphisms.- If
Pholds forf : X ⟶ Y, thenPholds forf ∣_ Y.basicOpen rfor any global sectionr. - If
Pholds forf ∣_ Y.basicOpen rfor allrin a spanning set of the global sections, thenPholds forf.
AlgebraicGeometry.PropertyIsLocalAtTarget: We say thatPropertyIsLocalAtTarget PforP : MorphismProperty Schemeif
Prespects isomorphisms.- If
Pholds forf : X ⟶ Y, thenPholds forf ∣_ Ufor anyU. - If
Pholds forf ∣_ Ufor an open coverUofY, thenPholds forf.
Main results #
AlgebraicGeometry.AffineTargetMorphismProperty.IsLocal.affine_openCover_TFAE: IfP.IsLocal, thentargetAffineLocally P fiff there exists an affine cover{ Uᵢ }ofYsuch thatPholds forf ∣_ Uᵢ.AlgebraicGeometry.AffineTargetMorphismProperty.isLocalOfOpenCoverImply: If the existence of an affine cover{ Uᵢ }ofYsuch thatPholds forf ∣_ UᵢimpliestargetAffineLocally P f, thenP.IsLocal.AlgebraicGeometry.AffineTargetMorphismProperty.IsLocal.affine_target_iff: IfYis affine andf : X ⟶ Y, thentargetAffineLocally P f ↔ P fprovidedP.IsLocal.AlgebraicGeometry.AffineTargetMorphismProperty.IsLocal.targetAffineLocallyIsLocal: IfP.IsLocal, thenPropertyIsLocalAtTarget (targetAffineLocally P).AlgebraicGeometry.PropertyIsLocalAtTarget.openCover_TFAE: IfPropertyIsLocalAtTarget P, thenP fiff there exists an open cover{ Uᵢ }ofYsuch thatPholds forf ∣_ Uᵢ.
These results should not be used directly, and should be ported to each property that is local.
An AffineTargetMorphismProperty is a class of morphisms from an arbitrary scheme into an
affine scheme.
Equations
- AlgebraicGeometry.AffineTargetMorphismProperty = (⦃X Y : AlgebraicGeometry.Scheme⦄ → (X ⟶ Y) → [inst : AlgebraicGeometry.IsAffine Y] → Prop)
Instances For
IsIso as a MorphismProperty.
Equations
Instances For
IsIso as an AffineTargetMorphismProperty.
Instances For
An AffineTargetMorphismProperty can be extended to a MorphismProperty such that it
never holds when the target is not affine
Equations
- AlgebraicGeometry.AffineTargetMorphismProperty.toProperty P f = ∃ (h : AlgebraicGeometry.IsAffine x), P f
Instances For
For a P : AffineTargetMorphismProperty, targetAffineLocally P holds for
f : X ⟶ Y whenever P holds for the restriction of f on every affine open subset of Y.
Equations
- AlgebraicGeometry.targetAffineLocally P f = ∀ (U : ↑(AlgebraicGeometry.Scheme.affineOpens Y)), P (f ∣_ ↑U)
Instances For
We say that P : AffineTargetMorphismProperty is a local property if
Prespects isomorphisms.- If
Pholds forf : X ⟶ Y, thenPholds forf ∣_ Y.basicOpen rfor any global sectionr. - If
Pholds forf ∣_ Y.basicOpen rfor allrin a spanning set of the global sections, thenPholds forf.
- RespectsIso : CategoryTheory.MorphismProperty.RespectsIso (AlgebraicGeometry.AffineTargetMorphismProperty.toProperty P)
Pas a morphism property respects isomorphisms - toBasicOpen : ∀ {X Y : AlgebraicGeometry.Scheme} [inst : AlgebraicGeometry.IsAffine Y] (f : X ⟶ Y) (r : ↑(Y.presheaf.obj (Opposite.op ⊤))), P f → P (f ∣_ Y.basicOpen r)
Pis stable under restriction to basic open set of global sections. - ofBasicOpenCover : ∀ {X Y : AlgebraicGeometry.Scheme} [inst : AlgebraicGeometry.IsAffine Y] (f : X ⟶ Y) (s : Finset ↑(Y.presheaf.obj (Opposite.op ⊤))), Ideal.span ↑s = ⊤ → (∀ (r : { x : ↑(Y.presheaf.obj (Opposite.op ⊤)) // x ∈ s }), P (f ∣_ Y.basicOpen ↑r)) → P f
PforfifPholds forfrestricted to basic sets of a spanning set of the global sections
Instances For
Specialization of ConcreteCategory.id_apply because simp can't see through the defeq.
We say that P : MorphismProperty Scheme is local at the target if
Prespects isomorphisms.- If
Pholds forf : X ⟶ Y, thenPholds forf ∣_ Ufor anyU. - If
Pholds forf ∣_ Ufor an open coverUofY, thenPholds forf.
- RespectsIso : CategoryTheory.MorphismProperty.RespectsIso P
Prespects isomorphisms. - restrict : ∀ {X Y : AlgebraicGeometry.Scheme} (f : X ⟶ Y) (U : TopologicalSpace.Opens ↑↑Y.toPresheafedSpace), P f → P (f ∣_ U)
If
Pholds forf : X ⟶ Y, thenPholds forf ∣_ Ufor anyU. - of_openCover : ∀ {X Y : AlgebraicGeometry.Scheme} (f : X ⟶ Y) (𝒰 : AlgebraicGeometry.Scheme.OpenCover Y), (∀ (i : 𝒰.J), P CategoryTheory.Limits.pullback.snd) → P f
If
Pholds forf ∣_ Ufor an open coverUofY, thenPholds forf.
Instances For
A P : AffineTargetMorphismProperty is stable under base change if P holds for Y ⟶ S
implies that P holds for X ×ₛ Y ⟶ X with X and S affine schemes.
Equations
- One or more equations did not get rendered due to their size.
Instances For
The AffineTargetMorphismProperty associated to (targetAffineLocally P).diagonal.
See diagonal_targetAffineLocally_eq_targetAffineLocally.
Equations
- One or more equations did not get rendered due to their size.
Instances For
topologically P holds for a morphism if the underlying topological map satisfies P.
Equations
- AlgebraicGeometry.MorphismProperty.topologically P f = P ⇑f.val.base