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Mathlib.AlgebraicTopology.SimplexCategory.Augmented

The Augmented simplex category #

This file defines the AugmentedSimplexCategory as the category obtained by adding an initial object to SimplexCategory (using CategoryTheory.WithInitial).

This definition provides a canonical full and faithful inclusion functor inclusion : SimplexCategoryAugmentedSimplexCategory.

We prove that functors out of AugmentedSimplexCategory are equivalent to augmented cosimplicial objects and that functors out of AugmentedSimplexCategoryᵒᵖ are equivalent to augmented simplicial objects, and we provide a translation of the main constrcutions on augmented (co)simplicial objects (i.e drop, point and toArrow) in terms of these equivalences.

TODOs #

The AugmentedSimplexCategory is the category obtained from SimplexCategory by adjoining an initial object.

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    @[simp]
    theorem AugmentedSimplexCategory.inclusion_map {X✝ Y✝ : SimplexCategory} (f : X✝ Y✝) :

    Through the equivalence (AugmentedSimplexCategory ⥤ C) ≌ CosimplicialObject.Augmented C, dropping the augmentation corresponds to precomposition with inclusion : SimplexCategoryAugmentedSimplexCategory.

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      Through the equivalence (AugmentedSimplexCategory ⥤ C) ≌ CosimplicialObject.Augmented C, taking the point of the augmentation corresponds to evaluation at the initial object.

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        Through the equivalence (AugmentedSimplexCategory ⥤ C) ≌ CosimplicialObject.Augmented C, the arrow attached to the cosimplicial object is the one obtained by evaluation at the unique arrow star ⟶ of [0].

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          @[simp]
          theorem AugmentedSimplexCategory.equivAugmentedSimplicialObject_counitIso_inv_app_left_app {C : Type u_1} [CategoryTheory.Category.{u_2, u_1} C] (X : CategoryTheory.SimplicialObject.Augmented C) (X✝ : SimplexCategoryᵒᵖ) :
          @[simp]
          theorem AugmentedSimplexCategory.equivAugmentedSimplicialObject_inverse_obj_map {C : Type u_1} [CategoryTheory.Category.{u_2, u_1} C] (X : CategoryTheory.SimplicialObject.Augmented C) {X✝ Y✝ : (CategoryTheory.WithInitial SimplexCategory)ᵒᵖ} (f : X✝ Y✝) :

          Through the equivalence (AugmentedSimplexCategoryᵒᵖ ⥤ C) ≌ SimplicialObject.Augmented C, dropping the augmentation corresponds to precomposition with inclusionᵒᵖ : SimplexCategoryᵒᵖ ⥤ AugmentedSimplexCategoryᵒᵖ.

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            Through the equivalence (AugmentedSimplexCategory ⥤ C) ≌ CosimplicialObject.Augmented C, taking the point of the augmentation corresponds to evaluation at the initial object.

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              Through the equivalence (AugmentedSimplexCategory ⥤ C) ≌ CosimplicialObject.Augmented C, the arrow attached to the cosimplicial object is the one obtained by evaluation at the unique arrow star ⟶ of [0].

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