@@ -3,118 +3,6 @@ Copyright (c) 2025 Robin Carlier. All rights reserved.
33Released under Apache 2.0 license as described in the file LICENSE.
44Authors: Robin Carlier
55-/
6- import Mathlib.CategoryTheory.WithTerminal.Basic
7- import Mathlib.AlgebraicTopology.SimplexCategory.Basic
8- import Mathlib.AlgebraicTopology.SimplicialObject.Basic
6+ import Mathlib.AlgebraicTopology.SimplexCategory.Augmented.Basic
97
10- /-!
11- # The Augmented simplex category
12-
13- This file defines the `AugmentedSimplexCategory` as the category obtained by adding an initial
14- object to `SimplexCategory` (using `CategoryTheory.WithInitial`).
15-
16- This definition provides a canonical full and faithful inclusion functor
17- `inclusion : SimplexCategory ⥤ AugmentedSimplexCategory`.
18-
19- We prove that functors out of `AugmentedSimplexCategory` are equivalent to augmented cosimplicial
20- objects and that functors out of `AugmentedSimplexCategoryᵒᵖ` are equivalent to augmented simplicial
21- objects, and we provide a translation of the main constrcutions on augmented (co)simplicial objects
22- (i.e `drop`, `point` and `toArrow`) in terms of these equivalences.
23-
24- ## TODOs
25- * Define a monoidal structure on `AugmentedSimplexCategory`.
26- -/
27-
28- open CategoryTheory
29-
30- /-- The `AugmentedSimplexCategory` is the category obtained from `SimplexCategory` by adjoining an
31- initial object. -/
32- def AugmentedSimplexCategory := WithInitial SimplexCategory
33- deriving SmallCategory
34-
35- namespace AugmentedSimplexCategory
36-
37- variable {C : Type *} [Category C]
38-
39- /-- The canonical inclusion from `SimplexCategory` to `AugmentedSimplexCategory`. -/
40- @[simps!]
41- def inclusion : SimplexCategory ⥤ AugmentedSimplexCategory := WithInitial.incl
42-
43- instance : inclusion.Full := inferInstanceAs WithInitial.incl.Full
44- instance : inclusion.Faithful := inferInstanceAs WithInitial.incl.Faithful
45-
46- instance : Limits.HasInitial AugmentedSimplexCategory :=
47- inferInstanceAs <| Limits.HasInitial <| WithInitial _
48-
49- /-- The equivalence between functors out of `AugmentedSimplexCategory` and augmented
50- cosimplicial objects. -/
51- @[simps!]
52- def equivAugmentedCosimplicialObject :
53- (AugmentedSimplexCategory ⥤ C) ≌ CosimplicialObject.Augmented C :=
54- WithInitial.equivComma
55-
56- /-- Through the equivalence `(AugmentedSimplexCategory ⥤ C) ≌ CosimplicialObject.Augmented C`,
57- dropping the augmentation corresponds to precomposition with
58- `inclusion : SimplexCategory ⥤ AugmentedSimplexCategory`. -/
59- @[simps!]
60- def equivAugmentedCosimplicialObjectFunctorCompDropIso :
61- equivAugmentedCosimplicialObject.functor ⋙ CosimplicialObject.Augmented.drop ≅
62- (Functor.whiskeringLeft _ _ C).obj inclusion :=
63- .refl _
64-
65- /-- Through the equivalence `(AugmentedSimplexCategory ⥤ C) ≌ CosimplicialObject.Augmented C`,
66- taking the point of the augmentation corresponds to evaluation at the initial object. -/
67- @[simps!]
68- def equivAugmentedCosimplicialObjectFunctorCompPointIso :
69- equivAugmentedCosimplicialObject.functor ⋙ CosimplicialObject.Augmented.point ≅
70- ((evaluation _ _).obj .star : (AugmentedSimplexCategory ⥤ C) ⥤ C) :=
71- .refl _
72-
73- @[deprecated (since := "2025-08-22")] alias equivAugmentedCosimplicialObjecFunctorCompPointIso :=
74- equivAugmentedCosimplicialObjectFunctorCompPointIso
75-
76- /-- Through the equivalence `(AugmentedSimplexCategory ⥤ C) ≌ CosimplicialObject.Augmented C`,
77- the arrow attached to the cosimplicial object is the one obtained by evaluation at the unique arrow
78- `star ⟶ of [0]`. -/
79- @[simps!]
80- def equivAugmentedCosimplicialObjectFunctorCompToArrowIso :
81- equivAugmentedCosimplicialObject.functor ⋙ CosimplicialObject.Augmented.toArrow ≅
82- Functor.mapArrowFunctor _ C ⋙
83- (evaluation _ _ |>.obj <| .mk <| WithInitial.homTo <| .mk 0 ) :=
84- .refl _
85-
86- /-- The equivalence between functors out of `AugmentedSimplexCategory` and augmented simplicial
87- objects. -/
88- @[simps!]
89- def equivAugmentedSimplicialObject :
90- (AugmentedSimplexCategoryᵒᵖ ⥤ C) ≌ SimplicialObject.Augmented C :=
91- WithInitial.opEquiv SimplexCategory |>.congrLeft |>.trans WithTerminal.equivComma
92-
93- /-- Through the equivalence `(AugmentedSimplexCategoryᵒᵖ ⥤ C) ≌ SimplicialObject.Augmented C`,
94- dropping the augmentation corresponds to precomposition with
95- `inclusionᵒᵖ : SimplexCategoryᵒᵖ ⥤ AugmentedSimplexCategoryᵒᵖ`. -/
96- @[simps!]
97- def equivAugmentedSimplicialObjectFunctorCompDropIso :
98- equivAugmentedSimplicialObject.functor ⋙ SimplicialObject.Augmented.drop ≅
99- (Functor.whiskeringLeft _ _ C).obj inclusion.op :=
100- .refl _
101-
102- /-- Through the equivalence `(AugmentedSimplexCategory ⥤ C) ≌ CosimplicialObject.Augmented C`,
103- taking the point of the augmentation corresponds to evaluation at the initial object. -/
104- @[simps!]
105- def equivAugmentedSimplicialObjectFunctorCompPointIso :
106- equivAugmentedSimplicialObject.functor ⋙ SimplicialObject.Augmented.point ≅
107- (evaluation _ C).obj (.op .star) :=
108- .refl _
109-
110- /-- Through the equivalence `(AugmentedSimplexCategory ⥤ C) ≌ CosimplicialObject.Augmented C`,
111- the arrow attached to the cosimplicial object is the one obtained by evaluation at the unique arrow
112- `star ⟶ of [0]`. -/
113- @[simps!]
114- def equivAugmentedSimplicialObjectFunctorCompToArrowIso :
115- equivAugmentedSimplicialObject.functor ⋙ SimplicialObject.Augmented.toArrow ≅
116- Functor.mapArrowFunctor _ C ⋙
117- (evaluation _ _ |>.obj <| .mk <| .op <| WithInitial.homTo <| .mk 0 ) :=
118- .refl _
119-
120- end AugmentedSimplexCategory
8+ deprecated_module (since := "2025-07-05" )
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