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Mathlib.Topology.Category.TopCat.Adjunctions

Adjunctions regarding the category of topological spaces #

This file shows that the forgetful functor from topological spaces to types has a left and right adjoint, given by TopCat.discrete, resp. TopCat.trivial, the functors which equip a type with the discrete, resp. trivial, topology.

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@[simp]
theorem TopCat.adj₁_counit :
TopCat.adj₁.counit = { app := fun (X : TopCat) => { toFun := id, continuous_toFun := ⋯ }, naturality := TopCat.adj₁.proof_3 }
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@[simp]
theorem TopCat.adj₁_unit :
TopCat.adj₁.unit = { app := fun (X : Type u) => id, naturality := TopCat.adj₁.proof_1 }
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def TopCat.adj₁ :
TopCat.discrete ⊣ CategoryTheory.forget TopCat

Equipping a type with the discrete topology is left adjoint to the forgetful functor Top ⥤ Type.

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Instances For
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    @[simp]
    theorem TopCat.adj₂_counit :
    TopCat.adj₂.counit = { app := fun (X : Type u) => id, naturality := TopCat.adj₂.proof_3 }
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    @[simp]
    theorem TopCat.adj₂_unit :
    TopCat.adj₂.unit = { app := fun (X : TopCat) => { toFun := id, continuous_toFun := ⋯ }, naturality := TopCat.adj₂.proof_2 }
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    def TopCat.adj₂ :
    CategoryTheory.forget TopCat ⊣ TopCat.trivial

    Equipping a type with the trivial topology is right adjoint to the forgetful functor Top ⥤ Type.

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    Instances For
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      instance TopCat.instIsRightAdjointForget :
      (CategoryTheory.forget TopCat).IsRightAdjoint
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      instance TopCat.instIsLeftAdjointForget :
      (CategoryTheory.forget TopCat).IsLeftAdjoint
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