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chore(CategoryTheory/Adjunction): slightly generalize universes in adjoint functor theorem (leanprover-community#34541)
Also updates a name in the module docstring
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Mathlib/CategoryTheory/Adjunction/AdjointFunctorTheorems.lean

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@@ -17,7 +17,7 @@ public import Mathlib.CategoryTheory.Subobject.Comma
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This file proves the (general) adjoint functor theorem, in the form:
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* If `G : D ⥤ C` preserves limits and `D` has limits, and satisfies the solution set condition,
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then it has a left adjoint: `isRightAdjointOfPreservesLimitsOfIsCoseparating`.
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then it has a left adjoint: `isRightAdjoint_of_preservesLimits_of_isCoseparating`.
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We show that the converse holds, i.e. that if `G` has a left adjoint then it satisfies the solution
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set condition, see `solutionSetCondition_of_isRightAdjoint`
@@ -29,7 +29,7 @@ factors through one of the `f_i`.
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This file also proves the special adjoint functor theorem, in the form:
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* If `G : D ⥤ C` preserves limits and `D` is complete, well-powered and has a small coseparating
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set, then `G` has a left adjoint: `isRightAdjointOfPreservesLimitsOfIsCoseparating`
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set, then `G` has a left adjoint: `isRightAdjoint_of_preservesLimits_of_isCoseparating`
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Finally, we prove the following corollaries of the special adjoint functor theorem:
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* If `C` is complete, well-powered and has a small coseparating set, then it is cocomplete:
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@[expose] public section
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universe v u u'
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universe w v v₁ u u₁ u'
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namespace CategoryTheory
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@@ -59,18 +59,18 @@ The key part of this definition is that the indexing set `ι` lives in `Type v`,
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universe of morphisms of the category: this is the "smallness" condition which allows the general
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adjoint functor theorem to go through.
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-/
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def SolutionSetCondition {D : Type u} [Category.{v} D] (G : D ⥤ C) : Prop :=
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def SolutionSetCondition {D : Type u} [Category.{v} D] (G : D ⥤ C) : Prop :=
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∀ A : C,
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∃ (ι : Type v) (B : ι → D) (f : ∀ i : ι, A ⟶ G.obj (B i)),
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∃ (ι : Type w) (B : ι → D) (f : ∀ i : ι, A ⟶ G.obj (B i)),
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∀ (X) (h : A ⟶ G.obj X), ∃ (i : ι) (g : B i ⟶ X), f i ≫ G.map g = h
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section GeneralAdjointFunctorTheorem
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variable {D : Type u} [Category.{v} D]
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variable {D : Type u} [Category.{v} D]
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variable (G : D ⥤ C)
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/-- If `G : D ⥤ C` is a right adjoint it satisfies the solution set condition. -/
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theorem solutionSetCondition_of_isRightAdjoint [G.IsRightAdjoint] : SolutionSetCondition G := by
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theorem solutionSetCondition_of_isRightAdjoint [G.IsRightAdjoint] : SolutionSetCondition.{w} G := by
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intro A
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refine
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⟨PUnit, fun _ => G.leftAdjoint.obj A, fun _ => (Adjunction.ofIsRightAdjoint G).unit.app A, ?_⟩
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if `G` satisfies the solution set condition then `G` is a right adjoint.
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-/
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lemma isRightAdjoint_of_preservesLimits_of_solutionSetCondition [HasLimits D]
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[PreservesLimits G] (hG : SolutionSetCondition G) : G.IsRightAdjoint := by
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[PreservesLimitsOfSize.{v₁, v₁} G] (hG : SolutionSetCondition.{v₁} G) : G.IsRightAdjoint := by
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refine @isRightAdjointOfStructuredArrowInitials _ _ _ _ G ?_
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intro A
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specialize hG A

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