Module

FlatBaseChangeAffinization.lean

Nyll.SchemeTheory.Affine.FlatBaseChangeAffinization
2 declarations indexed from sourceView source ↗

Affinization commutes with flat affine base change

The qcqs theorem on sections gives an actual pushout square of global sections. Applying Spec and cancelling the affine base square proves that the canonical affinization map commutes with the given base change.

Declarations

AlgebraicGeometry.isPushout_appTop_of_flat

The actual maps on global sections form a pushout after flat affine base change of a qcqs morphism.

Source context 6 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
open CategoryTheory CategoryTheory.Limits TopologicalSpace
namespace AlgebraicGeometry
universe u
variable {X S T : Scheme.{u}} (f : X ⟶ S) (g : T ⟶ S)
variable [IsAffine S] [IsAffine T] [QuasiCompact f] [QuasiSeparated f] [Flat g]
theorem isPushout_appTop_of_flat :
    IsPushout f.appTop g.appTop (pullback.fst f g).appTop
      (pullback.snd f g).appTop
AlgebraicGeometry.isPullback_toSpecΓ_of_flat

The canonical affinization morphism is compatible with flat affine base change, as an actual cartesian square.

Source context 6 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
open CategoryTheory CategoryTheory.Limits TopologicalSpace
namespace AlgebraicGeometry
universe u
variable {X S T : Scheme.{u}} (f : X ⟶ S) (g : T ⟶ S)
variable [IsAffine S] [IsAffine T] [QuasiCompact f] [QuasiSeparated f] [Flat g]
theorem isPullback_toSpecΓ_of_flat :
    IsPullback (pullback f g).toSpecΓ (pullback.fst f g)
      (Spec.map (pullback.fst f g).appTop) X.toSpecΓ