@@ -113,9 +113,11 @@ instance (R : CommRingCatᵒᵖ) : IsAffine (Scheme.Spec.obj R) :=
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instance isAffine_Spec (R : CommRingCat) : IsAffine (Spec R) :=
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AlgebraicGeometry.isAffine_affineScheme ⟨_, Scheme.Spec.obj_mem_essImage (op R)⟩
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- theorem isAffine_of_isIso {X Y : Scheme} (f : X ⟶ Y) [IsIso f] [h : IsAffine Y] : IsAffine X := by
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+ theorem IsAffine.of_isIso {X Y : Scheme} (f : X ⟶ Y) [IsIso f] [h : IsAffine Y] : IsAffine X := by
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rw [← mem_Spec_essImage] at h ⊢; exact Functor.essImage.ofIso (asIso f).symm h
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+ @[deprecated (since := "2025-03-31")] alias isAffine_of_isIso := IsAffine.of_isIso
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+
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/-- If `f : X ⟶ Y` is a morphism between affine schemes, the corresponding arrow is isomorphic
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to the arrow of the morphism on prime spectra induced by the map on global sections. -/
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noncomputable
@@ -221,7 +223,7 @@ instance {Y : Scheme.{u}} (U : Y.affineOpens) : IsAffine U :=
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theorem isAffineOpen_opensRange {X Y : Scheme} [IsAffine X] (f : X ⟶ Y)
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[H : IsOpenImmersion f] : IsAffineOpen (Scheme.Hom.opensRange f) := by
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- refine isAffine_of_isIso (IsOpenImmersion.isoOfRangeEq f (Y.ofRestrict _) ?_).inv
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+ refine .of_isIso (IsOpenImmersion.isoOfRangeEq f (Y.ofRestrict _) ?_).inv
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exact Subtype.range_val.symm
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theorem isAffineOpen_top (X : Scheme) [IsAffine X] : IsAffineOpen (⊤ : X.Opens) := by
@@ -444,19 +446,19 @@ theorem image_of_isOpenImmersion (f : X ⟶ Y) [H : IsOpenImmersion f] :
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theorem preimage_of_isIso {U : Y.Opens} (hU : IsAffineOpen U) (f : X ⟶ Y) [IsIso f] :
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IsAffineOpen (f ⁻¹ᵁ U) :=
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haveI : IsAffine _ := hU
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- isAffine_of_isIso (f ∣_ U)
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+ .of_isIso (f ∣_ U)
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theorem _root_.AlgebraicGeometry.Scheme.Hom.isAffineOpen_iff_of_isOpenImmersion
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(f : AlgebraicGeometry.Scheme.Hom X Y) [H : IsOpenImmersion f] {U : X.Opens} :
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- IsAffineOpen (f ''ᵁ U) ↔ IsAffineOpen U := by
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- refine ⟨ fun hU => @isAffine_of_isIso _ _
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- (IsOpenImmersion.isoOfRangeEq (X.ofRestrict U.isOpenEmbedding ≫ f) (Y.ofRestrict _) ?_).hom
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- ?_ hU, fun hU => hU.image_of_isOpenImmersion f⟩
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- · rw [Scheme.comp_base, TopCat.coe_comp, Set.range_comp]
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+ IsAffineOpen (f ''ᵁ U) ↔ IsAffineOpen U where
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+ mp hU := by
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+ refine .of_isIso (IsOpenImmersion.isoOfRangeEq (X.ofRestrict U.isOpenEmbedding ≫ f)
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+ (Y.ofRestrict _) ?_).hom (h := hU)
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+ rw [Scheme.comp_base, TopCat.coe_comp, Set.range_comp]
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dsimp [Opens.coe_inclusion', Scheme.restrict]
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rw [Subtype.range_coe, Subtype.range_coe]
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rfl
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- · infer_instance
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+ mpr hU := hU.image_of_isOpenImmersion f
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/-- The affine open sets of an open subscheme corresponds to
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the affine open sets containing in the image. -/
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