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Mathlib.AlgebraicTopology.SimplicialSet.Monoidal

The monoidal category structure on simplicial sets #

This file defines an instance of chosen finite products for the category SSet. It follows from the fact the SSet if a category of functors to the category of types and that the category of types have chosen finite products. As a result, we obtain a monoidal category structure on SSet.

@[simp]

The bijection (𝟙_ SSet ⟶ K) ≃ K _⦋0⦌.

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    The external product of subcomplexes of simplicial sets.

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      @[simp]
      theorem SSet.Subcomplex.prod_obj {X Y : SSet} (A : X.Subcomplex) (B : Y.Subcomplex) (Δ : SimplexCategoryᵒᵖ) :
      (A.prod B).obj Δ = (A.obj Δ).prod (B.obj Δ)
      theorem SSet.Subcomplex.prod_monotone {X Y : SSet} {A₁ A₂ : X.Subcomplex} (hX : A₁ A₂) {B₁ B₂ : Y.Subcomplex} (hY : B₁ B₂) :
      A₁.prod B₁ A₂.prod B₂
      theorem SSet.Subcomplex.range_tensorHom {X₁ X₂ Y₁ Y₂ : SSet} (f₁ : X₁ Y₁) (f₂ : X₂ Y₂) :

      The isomorphism (A.prod B).toSSet ≅ A.toSSet ⊗ B.toSSet.

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        The inclusion X ⟶ X ⊗ Δ[1] which is 0 on the second factor.

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          @[simp]
          theorem SSet.ι₀_app_fst {X : SSet} {m : SimplexCategoryᵒᵖ} (x : X.obj m) :
          (ι₀.app m x).1 = x
          @[simp]
          theorem SSet.ι₀_app_snd_apply {X : SSet} {m : } (x : X.obj (Opposite.op (SimplexCategory.mk m))) (k : Fin (m + 1)) :

          The inclusion X ⟶ X ⊗ Δ[1] which is 1 on the second factor.

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            @[simp]
            theorem SSet.ι₁_app_fst {X : SSet} {m : SimplexCategoryᵒᵖ} (x : X.obj m) :
            (ι₁.app m x).1 = x
            @[simp]
            theorem SSet.ι₁_app_snd_apply {X : SSet} {m : } (x : X.obj (Opposite.op (SimplexCategory.mk m))) (k : Fin (m + 1)) :

            Given S ≤ X and T ≤ Y, this is the subcomplex of X ⊗ Y given by (X ⊗ T) ⊔ (S ⊗ Y).

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              The inclusion X ⊗ T ⟶ S.unionProd T as simplicial sets.

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                The inclusion S ⊗ Y ⟶ S.unionProd T as simplicial sets

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                  @[simp]
                  @[simp]
                  noncomputable def SSet.Subcomplex.unionProd.symmIso {X Y : SSet} (S : X.Subcomplex) (T : Y.Subcomplex) :

                  The isomorphism unionProd S T ≅ unionProd T S as simplicial sets.

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                    @[implicit_reducible]