Documentation

Mathlib.AlgebraicGeometry.OpenImmersion

Open immersions of schemes #

@[reducible, inline]

A morphism of Schemes is an open immersion if it is an open immersion as a morphism of LocallyRingedSpaces

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      To show that a locally ringed space is a scheme, it suffices to show that it has a jointly surjective family of open immersions from affine schemes.

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          The image of an open immersion as an open set.

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              @[reducible, inline]

              The functor opens X ⥤ opens Y associated with an open immersion f : X ⟶ Y.

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                  f ''ᵁ U is notation for the image (as an open set) of U under an open immersion f.

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                      theorem AlgebraicGeometry.Scheme.Hom.image_iSup {X Y : Scheme} (f : X.Hom Y) [H : IsOpenImmersion f] {ι : Sort u_1} (s : ιX.Opens) :
                      f.opensFunctor.obj (⨆ (i : ι), s i) = ⨆ (i : ι), f.opensFunctor.obj (s i)
                      theorem AlgebraicGeometry.Scheme.Hom.image_iSup₂ {X Y : Scheme} (f : X.Hom Y) [H : IsOpenImmersion f] {ι : Sort u_1} {κ : ιSort u_2} (s : (i : ι) → κ iX.Opens) :
                      f.opensFunctor.obj (⨆ (i : ι), ⨆ (j : κ i), s i j) = ⨆ (i : ι), ⨆ (j : κ i), f.opensFunctor.obj (s i j)

                      The isomorphism Γ(Y, f(U)) ≅ Γ(X, U) induced by an open immersion f : X ⟶ Y.

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                          theorem AlgebraicGeometry.Scheme.Hom.appIso_hom' {X Y : Scheme} (f : X.Hom Y) [H : IsOpenImmersion f] (U : X.Opens) :
                          (f.appIso U).hom = f.appLE (f.opensFunctor.obj U) U

                          A variant of app_invApp that gives an eqToHom instead of homOfLE.

                          The open sets of an open subscheme corresponds to the open sets containing in the image.

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                              If X ⟶ Y is an open immersion, and Y is a scheme, then so is X.

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                                  If X ⟶ Y is an open immersion of PresheafedSpaces, and Y is a Scheme, we can upgrade it into a morphism of Schemes.

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                                      The restriction of a Scheme along an open embedding.

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                                          The canonical map from the restriction to the subspace.

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                                              An open immersion induces an isomorphism from the domain onto the image

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                                                  The universal property of open immersions: For an open immersion f : X ⟶ Z, given any morphism of schemes g : Y ⟶ Z whose topological image is contained in the image of f, we can lift this morphism to a unique Y ⟶ X that commutes with these maps.

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                                                      Two open immersions with equal range are isomorphic.

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                                                          If f is an open immersion X ⟶ Y, the global sections of X are naturally isomorphic to the sections of Y over the image of f.

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                                                              Given an open immersion f : U ⟶ X, the isomorphism between global sections of U and the sections of X at the image of f.

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