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Mathlib.Algebra.Category.MonCat.ForgetCorepresentable

The forget 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_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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    @[simp]
    theorem uliftMultiplesHom_apply_apply (M : Type u) [AddMonoid M] (a✝ : M) (a✝¹ : ULift.{u, 0} ℕ) :
    ((uliftMultiplesHom M) a✝) a✝¹ = AddEquiv.ulift a✝¹ • a✝
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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_apply_apply (M : Type u) [Monoid M] (a✝ : M) (a✝¹ : ULift.{u, 0} (Multiplicative ℕ)) :
      ((uliftPowersHom M) a✝) a✝¹ = a✝ ^ Multiplicative.toAdd (MulEquiv.ulift a✝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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      @[deprecated powersHom (since := "2025-05-11")]
      def MonoidHom.fromMultiplicativeNatEquiv (α : Type u) [Monoid α] :
      (Multiplicative ℕ →* α) ≃ α

      The equivalence (Multiplicative ℕ →* α) ≃ α for any monoid α.

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        @[deprecated uliftPowersHom (since := "2025-05-11")]
        def MonoidHom.fromULiftMultiplicativeNatEquiv (α : Type u) [Monoid α] :
        (ULift.{u, 0} (Multiplicative ℕ) →* α) ≃ α

        The equivalence (ULift (Multiplicative ℕ) →* α) ≃ α for any monoid α.

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          @[deprecated multiplesHom (since := "2025-05-11")]
          def AddMonoidHom.fromNatEquiv (α : Type u) [AddMonoid α] :
          (ℕ →+ α) ≃ α

          The equivalence (ℤ →+ α) ≃ α for any additive group α.

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            @[deprecated uliftMultiplesHom (since := "2025-05-11")]
            def AddMonoidHom.fromULiftNatEquiv (α : Type u) [AddMonoid α] :
            (ULift.{u, 0} ℕ →+ α) ≃ α

            The equivalence (ULift ℕ →+ α) ≃ α for any additive monoid α.

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              def MonCat.coyonedaObjIsoForget :
              CategoryTheory.coyoneda.obj (Opposite.op (of (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 (of (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 (of (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 (of (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