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Mathlib.Algebra.Category.MonCat.ForgetCorepresentable

The forgetful functor is corepresentable #

The forgetful functor AddCommMonCat.{u} ⥤ Type u is corepresentable by ULift ℕ. Similar results are obtained for the variants CommMonCat, AddMonCat and MonCat.

(ULift ℕ →+ G) ≃ G #

These universe-monomorphic variants of multiplesHom/powersHom are put here since they shouldn't be useful outside of category theory.

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def uliftMultiplesHom (M : Type u) [AddMonoid M] :
M ≃ (ULift.{u, 0} ℕ →+ M)

Monoid homomorphisms from ULift ℕ are defined by the image of 1.

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    @[simp]
    theorem uliftMultiplesHom_apply_apply (M : Type u) [AddMonoid M] (a✝ : M) (x : ULift.{u, 0} ℕ) :
    ((uliftMultiplesHom M) a✝) x = AddEquiv.ulift x • a✝
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    @[simp]
    theorem uliftMultiplesHom_symm_apply (M : Type u) [AddMonoid M] (a✝ : ULift.{u, 0} ℕ →+ M) :
    (uliftMultiplesHom M).symm a✝ = a✝ (AddEquiv.ulift.symm 1)
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    def uliftPowersHom (M : Type u) [Monoid M] :
    M ≃ (ULift.{u, 0} (Multiplicative ℕ) →* M)

    Monoid homomorphisms from ULift (Multiplicative ℕ) are defined by the image of Multiplicative.ofAdd 1.

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      @[simp]
      theorem uliftPowersHom_symm_apply (M : Type u) [Monoid M] (a✝ : ULift.{u, 0} (Multiplicative ℕ) →* M) :
      (uliftPowersHom M).symm a✝ = a✝ (MulEquiv.ulift.symm (Multiplicative.ofAdd 1))
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      @[simp]
      theorem uliftPowersHom_apply_apply (M : Type u) [Monoid M] (a✝ : M) (x : ULift.{u, 0} (Multiplicative ℕ)) :
      ((uliftPowersHom M) a✝) x = a✝ ^ Multiplicative.toAdd (MulEquiv.ulift x)
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      def MonCat.coyonedaObjIsoForget :
      CategoryTheory.coyoneda.obj (Opposite.op ↧(ULift.{u, 0} (Multiplicative ℕ))) ≅ CategoryTheory.forget MonCat

      The forgetful functor MonCat.{u} ⥤ Type u is corepresentable.

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        def CommMonCat.coyonedaObjIsoForget :
        CategoryTheory.coyoneda.obj (Opposite.op ↧(ULift.{u, 0} (Multiplicative ℕ))) ≅ CategoryTheory.forget CommMonCat

        The forgetful functor CommMonCat.{u} ⥤ Type u is corepresentable.

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          def AddMonCat.coyonedaObjIsoForget :
          CategoryTheory.coyoneda.obj (Opposite.op ↧(ULift.{u, 0} ℕ)) ≅ CategoryTheory.forget AddMonCat

          The forgetful functor AddMonCat.{u} ⥤ Type u is corepresentable.

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            def AddCommMonCat.coyonedaObjIsoForget :
            CategoryTheory.coyoneda.obj (Opposite.op ↧(ULift.{u, 0} ℕ)) ≅ CategoryTheory.forget AddCommMonCat

            The forgetful functor AddCommMonCat.{u} ⥤ Type u is corepresentable.

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              instance MonCat.forget_isCorepresentable :
              (CategoryTheory.forget MonCat).IsCorepresentable
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              instance CommMonCat.forget_isCorepresentable :
              (CategoryTheory.forget CommMonCat).IsCorepresentable
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              instance AddMonCat.forget_isCorepresentable :
              (CategoryTheory.forget AddMonCat).IsCorepresentable
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              instance AddCommMonCat.forget_isCorepresentable :
              (CategoryTheory.forget AddCommMonCat).IsCorepresentable