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Mathlib.AlgebraicGeometry.Morphisms.Basic

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 #

  1. P respects isomorphisms.
  2. If P holds for f : X ⟶ Y, then P holds for f ∣_ Y.basicOpen r for any global section r.
  3. If P holds for f ∣_ Y.basicOpen r for all r in a spanning set of the global sections, then P holds for f.
  1. P respects isomorphisms.
  2. If P holds for f : X ⟶ Y, then P holds for f ∣_ U for any U.
  3. If P holds for f ∣_ U for an open cover U of Y, then P holds for f.

Main results #

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.

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    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.

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      We say that P : AffineTargetMorphismProperty is a local property if

      1. P respects isomorphisms.
      2. If P holds for f : X ⟶ Y, then P holds for f ∣_ Y.basicOpen r for any global section r.
      3. If P holds for f ∣_ Y.basicOpen r for all r in a spanning set of the global sections, then P holds for f.
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        @[simp]

        Specialization of ConcreteCategory.id_apply because simp can't see through the defeq.

        theorem AlgebraicGeometry.AffineTargetMorphismProperty.IsLocal.affine_openCover_TFAE {P : AlgebraicGeometry.AffineTargetMorphismProperty} (hP : AlgebraicGeometry.AffineTargetMorphismProperty.IsLocal P) {X : AlgebraicGeometry.Scheme} {Y : AlgebraicGeometry.Scheme} (f : X Y) :
        List.TFAE [AlgebraicGeometry.targetAffineLocally P f, ∃ (𝒰 : AlgebraicGeometry.Scheme.OpenCover Y) (x : ∀ (i : 𝒰.J), AlgebraicGeometry.IsAffine (𝒰.obj i)), ∀ (i : 𝒰.J), P CategoryTheory.Limits.pullback.snd, ∀ (𝒰 : AlgebraicGeometry.Scheme.OpenCover Y) [inst : ∀ (i : 𝒰.J), AlgebraicGeometry.IsAffine (𝒰.obj i)] (i : 𝒰.J), P CategoryTheory.Limits.pullback.snd, ∀ {U : AlgebraicGeometry.Scheme} (g : U Y) [inst : AlgebraicGeometry.IsAffine U] [inst_1 : AlgebraicGeometry.IsOpenImmersion g], P CategoryTheory.Limits.pullback.snd, ∃ (ι : Type u) (U : ιTopologicalSpace.Opens Y.toPresheafedSpace) (_ : iSup U = ) (hU' : ∀ (i : ι), AlgebraicGeometry.IsAffineOpen (U i)), ∀ (i : ι), P (f ∣_ U i)]

        We say that P : MorphismProperty Scheme is local at the target if

        1. P respects isomorphisms.
        2. If P holds for f : X ⟶ Y, then P holds for f ∣_ U for any U.
        3. If P holds for f ∣_ U for an open cover U of Y, then P holds for f.
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          theorem AlgebraicGeometry.PropertyIsLocalAtTarget.openCover_TFAE {P : CategoryTheory.MorphismProperty AlgebraicGeometry.Scheme} (hP : AlgebraicGeometry.PropertyIsLocalAtTarget P) {X : AlgebraicGeometry.Scheme} {Y : AlgebraicGeometry.Scheme} (f : X Y) :
          List.TFAE [P f, ∃ (𝒰 : AlgebraicGeometry.Scheme.OpenCover Y), ∀ (i : 𝒰.J), P CategoryTheory.Limits.pullback.snd, ∀ (𝒰 : AlgebraicGeometry.Scheme.OpenCover Y) (i : 𝒰.J), P CategoryTheory.Limits.pullback.snd, ∀ (U : TopologicalSpace.Opens Y.toPresheafedSpace), P (f ∣_ U), ∀ {U : AlgebraicGeometry.Scheme} (g : U Y) [inst : AlgebraicGeometry.IsOpenImmersion g], P CategoryTheory.Limits.pullback.snd, ∃ (ι : Type u) (U : ιTopologicalSpace.Opens Y.toPresheafedSpace) (_ : iSup U = ), ∀ (i : ι), P (f ∣_ U i)]

          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.

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            theorem AlgebraicGeometry.diagonalTargetAffineLocallyOfOpenCover (P : AlgebraicGeometry.AffineTargetMorphismProperty) (hP : AlgebraicGeometry.AffineTargetMorphismProperty.IsLocal P) {X : AlgebraicGeometry.Scheme} {Y : AlgebraicGeometry.Scheme} (f : X Y) (𝒰 : AlgebraicGeometry.Scheme.OpenCover Y) [∀ (i : 𝒰.J), AlgebraicGeometry.IsAffine (𝒰.obj i)] (𝒰' : (i : 𝒰.J) → AlgebraicGeometry.Scheme.OpenCover (CategoryTheory.Limits.pullback f (𝒰.map i))) [∀ (i : 𝒰.J) (j : (𝒰' i).J), AlgebraicGeometry.IsAffine ((𝒰' i).obj j)] (h𝒰' : ∀ (i : 𝒰.J) (j k : (𝒰' i).J), P (CategoryTheory.Limits.pullback.mapDesc ((𝒰' i).map j) ((𝒰' i).map k) CategoryTheory.Limits.pullback.snd)) :
            theorem AlgebraicGeometry.AffineTargetMorphismProperty.IsLocal.diagonal_affine_openCover_TFAE {P : AlgebraicGeometry.AffineTargetMorphismProperty} (hP : AlgebraicGeometry.AffineTargetMorphismProperty.IsLocal P) {X : AlgebraicGeometry.Scheme} {Y : AlgebraicGeometry.Scheme} (f : X Y) :
            List.TFAE [CategoryTheory.MorphismProperty.diagonal (AlgebraicGeometry.targetAffineLocally P) f, ∃ (𝒰 : AlgebraicGeometry.Scheme.OpenCover Y) (x : ∀ (i : 𝒰.J), AlgebraicGeometry.IsAffine (𝒰.obj i)), ∀ (i : 𝒰.J), AlgebraicGeometry.AffineTargetMorphismProperty.diagonal P CategoryTheory.Limits.pullback.snd, ∀ (𝒰 : AlgebraicGeometry.Scheme.OpenCover Y) [inst : ∀ (i : 𝒰.J), AlgebraicGeometry.IsAffine (𝒰.obj i)] (i : 𝒰.J), AlgebraicGeometry.AffineTargetMorphismProperty.diagonal P CategoryTheory.Limits.pullback.snd, ∀ {U : AlgebraicGeometry.Scheme} (g : U Y) [inst : AlgebraicGeometry.IsAffine U] [inst_1 : AlgebraicGeometry.IsOpenImmersion g], AlgebraicGeometry.AffineTargetMorphismProperty.diagonal P CategoryTheory.Limits.pullback.snd, ∃ (𝒰 : AlgebraicGeometry.Scheme.OpenCover Y) (x : ∀ (i : 𝒰.J), AlgebraicGeometry.IsAffine (𝒰.obj i)) (𝒰' : (i : 𝒰.J) → AlgebraicGeometry.Scheme.OpenCover (CategoryTheory.Limits.pullback f (𝒰.map i))) (x_1 : ∀ (i : 𝒰.J) (j : (𝒰' i).J), AlgebraicGeometry.IsAffine ((𝒰' i).obj j)), ∀ (i : 𝒰.J) (j k : (𝒰' i).J), P (CategoryTheory.Limits.pullback.mapDesc ((𝒰' i).map j) ((𝒰' i).map k) CategoryTheory.Limits.pullback.snd)]

            topologically P holds for a morphism if the underlying topological map satisfies P.

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