Mercurial > hg > Members > kono > Proof > category
annotate yoneda.agda @ 660:b9358172faf2
add maybe-monad
author | Shinji KONO <kono@ie.u-ryukyu.ac.jp> |
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date | Wed, 19 Jul 2017 20:38:02 +0900 |
parents | c375d8f93a2c |
children | 984518c56e96 |
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1 --- |
189 | 2 -- |
3 -- A → Sets^A^op : Yoneda Functor | |
4 -- Contravariant Functor h_a | |
5 -- Nat(h_a,F) | |
6 -- Shinji KONO <kono@ie.u-ryukyu.ac.jp> | |
7 ---- | |
8 | |
178 | 9 open import Category -- https://github.com/konn/category-agda |
10 open import Level | |
11 open import Category.Sets | |
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12 module yoneda where |
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13 -- { c₁ c₂ ℓ : Level} { A : Category c₁ c₂ ℓ } where |
178 | 14 |
15 open import HomReasoning | |
16 open import cat-utility | |
179 | 17 open import Relation.Binary.Core |
18 open import Relation.Binary | |
19 | |
178 | 20 |
21 -- Contravariant Functor : op A → Sets ( Obj of Sets^{A^op} ) | |
197 | 22 -- Obj and Hom of Sets^A^op |
181 | 23 |
197 | 24 open Functor |
183
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25 |
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26 YObj : { c₁ c₂ ℓ : Level} ( A : Category c₁ c₂ ℓ ) → Set (suc ℓ ⊔ (suc (suc c₂) ⊔ suc c₁)) |
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27 YObj {_} {c₂} A = Functor (Category.op A) (Sets {c₂}) |
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28 YHom : { c₁ c₂ ℓ : Level} ( A : Category c₁ c₂ ℓ ) (f : YObj A ) → (g : YObj A ) → Set (suc ℓ ⊔ (suc (suc c₂) ⊔ suc c₁)) |
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29 YHom {_} {c₂} A f g = NTrans (Category.op A) (Sets {c₂}) f g |
184 | 30 |
31 open NTrans | |
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32 Yid : { c₁ c₂ ℓ : Level} ( A : Category c₁ c₂ ℓ ) {a : YObj A } → YHom A a a |
300 | 33 Yid {_} {c₂} A {a} = record { TMap = λ a → λ x → x ; isNTrans = isNTrans1 {a} } where |
34 isNTrans1 : {a : YObj A } → IsNTrans (Category.op A) (Sets {c₂}) a a (λ a → λ x → x ) | |
184 | 35 isNTrans1 {a} = record { commute = refl } |
36 | |
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37 _+_ : { c₁ c₂ ℓ : Level} { A : Category c₁ c₂ ℓ } {a b c : YObj A} → YHom A b c → YHom A a b → YHom A a c |
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38 _+_ {_} {c₂} {_} {A} {a} {b} {c} f g = record { TMap = λ x → Sets [ TMap f x o TMap g x ] ; isNTrans = isNTrans1 } where |
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39 commute1 : (a b c : YObj A ) (f : YHom A b c) (g : YHom A a b ) |
185 | 40 (a₁ b₁ : Obj (Category.op A)) (h : Hom (Category.op A) a₁ b₁) → |
41 Sets [ Sets [ FMap c h o Sets [ TMap f a₁ o TMap g a₁ ] ] ≈ | |
42 Sets [ Sets [ TMap f b₁ o TMap g b₁ ] o FMap a h ] ] | |
43 commute1 a b c f g a₁ b₁ h = let open ≈-Reasoning (Sets {c₂})in begin | |
44 Sets [ FMap c h o Sets [ TMap f a₁ o TMap g a₁ ] ] | |
45 ≈⟨ assoc {_} {_} {_} {_} {FMap c h } {TMap f a₁} {TMap g a₁} ⟩ | |
46 Sets [ Sets [ FMap c h o TMap f a₁ ] o TMap g a₁ ] | |
47 ≈⟨ car (nat f) ⟩ | |
48 Sets [ Sets [ TMap f b₁ o FMap b h ] o TMap g a₁ ] | |
49 ≈↑⟨ assoc {_} {_} {_} {_} { TMap f b₁} {FMap b h } {TMap g a₁}⟩ | |
50 Sets [ TMap f b₁ o Sets [ FMap b h o TMap g a₁ ] ] | |
51 ≈⟨ cdr {_} {_} {_} {_} {_} { TMap f b₁} (nat g) ⟩ | |
52 Sets [ TMap f b₁ o Sets [ TMap g b₁ o FMap a h ] ] | |
53 ≈↑⟨ assoc {_} {_} {_} {_} {TMap f b₁} {TMap g b₁} { FMap a h} ⟩ | |
54 Sets [ Sets [ TMap f b₁ o TMap g b₁ ] o FMap a h ] | |
55 ∎ | |
56 isNTrans1 : IsNTrans (Category.op A) (Sets {c₂}) a c (λ x → Sets [ TMap f x o TMap g x ]) | |
57 isNTrans1 = record { commute = λ {a₁ b₁ h} → commute1 a b c f g a₁ b₁ h } | |
184 | 58 |
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59 _==_ : { c₁ c₂ ℓ : Level} { A : Category c₁ c₂ ℓ } {a b : YObj A} → YHom A a b → YHom A a b → Set (c₂ ⊔ c₁) |
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60 _==_ {_} { c₂} {_} {A} f g = ∀{x : Obj (Category.op A)} → (Sets {c₂}) [ TMap f x ≈ TMap g x ] |
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61 |
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62 infix 4 _==_ |
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63 |
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64 isSetsAop : { c₁ c₂ ℓ : Level} ( A : Category c₁ c₂ ℓ ) → IsCategory (YObj A) (YHom A) _==_ _+_ ( Yid A ) |
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65 isSetsAop {_} {c₂} {_} A = |
300 | 66 record { isEquivalence = record {refl = refl ; trans = λ {i j k} → trans1 {_} {_} {i} {j} {k} ; sym = λ {i j} → sym1 {_} {_} {i} {j}} |
189 | 67 ; identityL = refl |
68 ; identityR = refl | |
69 ; o-resp-≈ = λ{a b c f g h i } → o-resp-≈ {a} {b} {c} {f} {g} {h} {i} | |
70 ; associative = refl | |
358 | 71 } where |
72 open ≈-Reasoning (Sets {c₂}) | |
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73 sym1 : {a b : YObj A } {i j : YHom A a b } → i == j → j == i |
358 | 74 sym1 {a} {b} {i} {j} eq {x} = sym eq |
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75 trans1 : {a b : YObj A } {i j k : YHom A a b} → i == j → j == k → i == k |
358 | 76 trans1 {a} {b} {i} {j} {k} i=j j=k {x} = trans-hom i=j j=k |
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77 o-resp-≈ : {A₁ B C : YObj A} {f g : YHom A A₁ B} {h i : YHom A B C} → |
189 | 78 f == g → h == i → h + f == i + g |
358 | 79 o-resp-≈ {a} {b} {c} {f} {g} {h} {i} f=g h=i {x} = resp f=g h=i |
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80 |
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81 SetsAop : { c₁ c₂ ℓ : Level} ( A : Category c₁ c₂ ℓ ) → Category (suc ℓ ⊔ (suc (suc c₂) ⊔ suc c₁)) (suc ℓ ⊔ (suc (suc c₂) ⊔ suc c₁)) (c₂ ⊔ c₁) |
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82 SetsAop {_} {c₂} {_} A = |
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83 record { Obj = YObj A |
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84 ; Hom = YHom A |
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85 ; _o_ = _+_ |
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86 ; _≈_ = _==_ |
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87 ; Id = Yid A |
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88 ; isCategory = isSetsAop A |
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89 } |
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90 |
197 | 91 -- A is Locally small |
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92 postulate ≈-≡ : { c₁ c₂ ℓ : Level} { A : Category c₁ c₂ ℓ } {a b : Obj A } { x y : Hom A a b } → (x≈y : A [ x ≈ y ]) → x ≡ y |
197 | 93 |
94 import Relation.Binary.PropositionalEquality | |
95 -- Extensionality a b = {A : Set a} {B : A → Set b} {f g : (x : A) → B x} → (∀ x → f x ≡ g x) → f ≡ g → ( λ x → f x ≡ λ x → g x ) | |
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96 postulate extensionality : { c₁ c₂ ℓ : Level} ( A : Category c₁ c₂ ℓ ) → Relation.Binary.PropositionalEquality.Extensionality c₂ c₂ |
197 | 97 |
98 | |
99 ---- | |
100 -- | |
101 -- Object mapping in Yoneda Functor | |
102 -- | |
103 ---- | |
104 | |
105 open import Function | |
106 | |
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107 y-obj : { c₁ c₂ ℓ : Level} ( A : Category c₁ c₂ ℓ ) (a : Obj A) → Functor (Category.op A) (Sets {c₂}) |
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108 y-obj {_} {c₂} {_} A a = record { |
197 | 109 FObj = λ b → Hom (Category.op A) a b ; |
110 FMap = λ {b c : Obj A } → λ ( f : Hom A c b ) → λ (g : Hom A b a ) → (Category.op A) [ f o g ] ; | |
111 isFunctor = record { | |
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112 identity = λ {b} → extensionality A ( λ x → lemma-y-obj1 {b} x ) ; |
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113 distr = λ {a} {b} {c} {f} {g} → extensionality A ( λ x → lemma-y-obj2 a b c f g x ) ; |
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114 ≈-cong = λ eq → extensionality A ( λ x → lemma-y-obj3 x eq ) |
197 | 115 } |
116 } where | |
117 lemma-y-obj1 : {b : Obj A } → (x : Hom A b a) → (Category.op A) [ id1 A b o x ] ≡ x | |
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118 lemma-y-obj1 {b} x = let open ≈-Reasoning (Category.op A) in ≈-≡ {_} {_} {_} {A} idL |
197 | 119 lemma-y-obj2 : (a₁ b c : Obj A) (f : Hom A b a₁) (g : Hom A c b ) → (x : Hom A a₁ a )→ |
120 Category.op A [ Category.op A [ g o f ] o x ] ≡ (Sets [ _[_o_] (Category.op A) g o _[_o_] (Category.op A) f ]) x | |
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121 lemma-y-obj2 a₁ b c f g x = let open ≈-Reasoning (Category.op A) in ≈-≡ {_} {_} {_} {A} ( begin |
197 | 122 Category.op A [ Category.op A [ g o f ] o x ] |
123 ≈↑⟨ assoc ⟩ | |
124 Category.op A [ g o Category.op A [ f o x ] ] | |
125 ≈⟨⟩ | |
126 ( λ x → Category.op A [ g o x ] ) ( ( λ x → Category.op A [ f o x ] ) x ) | |
127 ∎ ) | |
128 lemma-y-obj3 : {b c : Obj A} {f g : Hom A c b } → (x : Hom A b a ) → A [ f ≈ g ] → Category.op A [ f o x ] ≡ Category.op A [ g o x ] | |
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129 lemma-y-obj3 {_} {_} {f} {g} x eq = let open ≈-Reasoning (Category.op A) in ≈-≡ {_} {_} {_} {A} ( begin |
197 | 130 Category.op A [ f o x ] |
131 ≈⟨ resp refl-hom eq ⟩ | |
132 Category.op A [ g o x ] | |
133 ∎ ) | |
134 | |
135 | |
136 ---- | |
137 -- | |
138 -- Hom mapping in Yoneda Functor | |
139 -- | |
140 ---- | |
141 | |
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142 y-tmap : { c₁ c₂ ℓ : Level} ( A : Category c₁ c₂ ℓ ) ( a b : Obj A ) → (f : Hom A a b ) → (x : Obj (Category.op A)) → |
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143 FObj (y-obj A a) x → FObj (y-obj A b ) x |
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144 y-tmap {_} {c₂} {_} A a b f x = λ ( g : Hom A x a ) → A [ f o g ] -- ( h : Hom A x b ) |
197 | 145 |
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146 y-map : { c₁ c₂ ℓ : Level} ( A : Category c₁ c₂ ℓ ) {a b : Obj A } → (f : Hom A a b ) → YHom A (y-obj A a) (y-obj A b) |
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147 y-map {_} {c₂} {_} A {a} {b} f = record { TMap = y-tmap A a b f ; isNTrans = isNTrans1 {a} {b} f } where |
197 | 148 lemma-y-obj4 : {a₁ b₁ : Obj (Category.op A)} {g : Hom (Category.op A) a₁ b₁} → {a b : Obj A } → (f : Hom A a b ) → |
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149 Sets [ Sets [ FMap (y-obj A b) g o y-tmap A a b f a₁ ] ≈ |
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150 Sets [ y-tmap A a b f b₁ o FMap (y-obj A a) g ] ] |
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151 lemma-y-obj4 {a₁} {b₁} {g} {a} {b} f = let open ≈-Reasoning A in extensionality A ( λ x → ≈-≡ {_} {_} {_} {A} ( begin |
197 | 152 A [ A [ f o x ] o g ] |
153 ≈↑⟨ assoc ⟩ | |
154 A [ f o A [ x o g ] ] | |
155 ∎ ) ) | |
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156 isNTrans1 : {a b : Obj A } → (f : Hom A a b ) → IsNTrans (Category.op A) (Sets {c₂}) (y-obj A a) (y-obj A b) (y-tmap A a b f ) |
197 | 157 isNTrans1 {a} {b} f = record { commute = λ{a₁ b₁ g } → lemma-y-obj4 {a₁} {b₁} {g} {a} {b} f } |
158 | |
159 ----- | |
160 -- | |
161 -- Yoneda Functor itself | |
162 -- | |
163 ----- | |
164 | |
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165 YonedaFunctor : { c₁ c₂ ℓ : Level} ( A : Category c₁ c₂ ℓ ) → Functor A (SetsAop A) |
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166 YonedaFunctor {_} {c₂} {_} A = record { |
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167 FObj = λ a → y-obj A a |
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168 ; FMap = λ f → y-map A f |
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169 ; isFunctor = record { |
187 | 170 identity = identity |
171 ; distr = distr1 | |
172 ; ≈-cong = ≈-cong | |
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173 |
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174 } |
187 | 175 } where |
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176 ≈-cong : {a b : Obj A} {f g : Hom A a b} → A [ f ≈ g ] → SetsAop A [ y-map A f ≈ y-map A g ] |
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177 ≈-cong {a} {b} {f} {g} eq = let open ≈-Reasoning (A) in -- (λ x g₁ → A [ f o g₁ ] ) ≡ (λ x g₁ → A [ g o g₁ ] ) |
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178 extensionality A ( λ h → ≈-≡ {_} {_} {_} {A} ( begin |
188
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179 A [ f o h ] |
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180 ≈⟨ resp refl-hom eq ⟩ |
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181 A [ g o h ] |
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182 ∎ |
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183 ) ) |
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184 identity : {a : Obj A} → SetsAop A [ y-map A (id1 A a) ≈ id1 (SetsAop A) (y-obj A a ) ] |
188
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185 identity {a} = let open ≈-Reasoning (A) in -- (λ x g → A [ id1 A a o g ] ) ≡ (λ a₁ x → x) |
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186 extensionality A ( λ g → ≈-≡ {_} {_} {_} {A} ( begin |
188
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187 A [ id1 A a o g ] |
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188 ≈⟨ idL ⟩ |
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189 g |
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190 ∎ |
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191 ) ) |
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192 distr1 : {a b c : Obj A} {f : Hom A a b} {g : Hom A b c} → SetsAop A [ y-map A (A [ g o f ]) ≈ SetsAop A [ y-map A g o y-map A f ] ] |
191 | 193 distr1 {a} {b} {c} {f} {g} = let open ≈-Reasoning (A) in -- (λ x g₁ → (A [ (A [ g o f] o g₁ ]))) ≡ (λ x x₁ → A [ g o A [ f o x₁ ] ] ) |
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194 extensionality A ( λ h → ≈-≡ {_} {_} {_} {A} ( begin |
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195 A [ A [ g o f ] o h ] |
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196 ≈↑⟨ assoc ⟩ |
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197 A [ g o A [ f o h ] ] |
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198 ∎ |
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199 ) ) |
184 | 200 |
185 | 201 |
190 | 202 ------ |
203 -- | |
204 -- F : A → Sets ∈ Obj SetsAop | |
205 -- | |
300 | 206 -- F(a) → Nat(h_a,F) |
191 | 207 -- x ∈ F(a) , (g : Hom A b a) → ( FMap F g ) x |
190 | 208 ------ |
187 | 209 |
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210 F2Natmap : { c₁ c₂ ℓ : Level} ( A : Category c₁ c₂ ℓ ) {a : Obj A} → {F : Obj ( SetsAop A) } |
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211 → {x : FObj F a} → (b : Obj (Category.op A)) → Hom Sets (FObj (y-obj A a) b) (FObj F b) |
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212 F2Natmap A {a} {F} {x} b = λ ( g : Hom A b a ) → ( FMap F g ) x |
190 | 213 |
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214 F2Nat : { c₁ c₂ ℓ : Level} ( A : Category c₁ c₂ ℓ ) {a : Obj A} → {F : Obj (SetsAop A )} → FObj F a → Hom (SetsAop A) (y-obj A a) F |
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215 F2Nat {_} {c₂} A {a} {F} x = record { TMap = F2Natmap A {a} {F} {x} ; isNTrans = isNTrans1 } where |
192
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216 commute1 : {a₁ b : Obj (Category.op A)} {f : Hom (Category.op A) a₁ b} (g : Hom A a₁ a) → |
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217 (Sets [ FMap F f o FMap F g ]) x ≡ FMap F (A [ g o f ] ) x |
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218 commute1 g = let open ≈-Reasoning (Sets) in |
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219 cong ( λ f → f x ) ( sym ( distr F ) ) |
191 | 220 commute : {a₁ b : Obj (Category.op A)} {f : Hom (Category.op A) a₁ b} → |
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221 Sets [ Sets [ FMap F f o F2Natmap A {a} {F} {x} a₁ ] ≈ Sets [ F2Natmap A {a} {F} {x} b o FMap (y-obj A a) f ] ] |
192
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222 commute {a₁} {b} {f} = let open ≈-Reasoning (Sets) in |
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223 begin |
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224 Sets [ FMap F f o F2Natmap A {a} {F} {x} a₁ ] |
192
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225 ≈⟨⟩ |
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226 Sets [ FMap F f o (λ ( g : Hom A a₁ a ) → ( FMap F g ) x) ] |
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227 ≈⟨ extensionality A ( λ (g : Hom A a₁ a) → commute1 {a₁} {b} {f} g ) ⟩ |
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228 Sets [ (λ ( g : Hom A b a ) → ( FMap F g ) x) o FMap (y-obj A a) f ] |
192
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229 ≈⟨⟩ |
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230 Sets [ F2Natmap A {a} {F} {x} b o FMap (y-obj A a) f ] |
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231 ∎ |
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232 isNTrans1 : IsNTrans (Category.op A) (Sets {c₂}) (y-obj A a) F (F2Natmap A {a} {F}) |
191 | 233 isNTrans1 = record { commute = λ {a₁ b f} → commute {a₁} {b} {f} } |
190 | 234 |
235 | |
199 | 236 -- F(a) <- Nat(h_a,F) |
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237 Nat2F : { c₁ c₂ ℓ : Level} ( A : Category c₁ c₂ ℓ ) {a : Obj A} → {F : Obj (SetsAop A) } → Hom (SetsAop A) (y-obj A a) F → FObj F a |
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238 Nat2F A {a} {F} ha = ( TMap ha a ) (id1 A a) |
190 | 239 |
199 | 240 ---- |
241 -- | |
242 -- Prove Bijection (as routine exercise ...) | |
243 -- | |
244 ---- | |
245 | |
299
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246 F2Nat→Nat2F : { c₁ c₂ ℓ : Level} ( A : Category c₁ c₂ ℓ ) {a : Obj A } → {F : Obj (SetsAop A)} → (fa : FObj F a) |
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247 → Nat2F A {a} {F} (F2Nat A {a} {F} fa) ≡ fa |
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248 F2Nat→Nat2F A {a} {F} fa = let open ≈-Reasoning (Sets) in cong ( λ f → f fa ) ( |
199 | 249 -- FMap F (Category.Category.Id A) fa ≡ fa |
194 | 250 begin |
251 ( FMap F (id1 A _ )) | |
252 ≈⟨ IsFunctor.identity (isFunctor F) ⟩ | |
253 id1 Sets (FObj F a) | |
254 ∎ ) | |
255 | |
256 open import Relation.Binary.PropositionalEquality | |
257 | |
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258 ≡-cong = Relation.Binary.PropositionalEquality.cong |
193
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259 |
195 | 260 -- F : op A → Sets |
197 | 261 -- ha : NTrans (op A) Sets (y-obj {a}) F |
262 -- FMap F g o TMap ha a ≈ TMap ha b o FMap (y-obj {a}) g | |
195 | 263 |
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264 Nat2F→F2Nat : { c₁ c₂ ℓ : Level} ( A : Category c₁ c₂ ℓ ) {a : Obj A } → {F : Obj (SetsAop A)} → (ha : Hom (SetsAop A) (y-obj A a) F) |
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265 → SetsAop A [ F2Nat A {a} {F} (Nat2F A {a} {F} ha) ≈ ha ] |
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266 Nat2F→F2Nat A {a} {F} ha {b} = let open ≡-Reasoning in |
194 | 267 begin |
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268 TMap (F2Nat A {a} {F} (Nat2F A {a} {F} ha)) b |
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269 ≡⟨⟩ |
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270 (λ g → FMap F g (TMap ha a (Category.Category.Id A))) |
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271 ≡⟨ extensionality A (λ g → ( |
195 | 272 begin |
273 FMap F g (TMap ha a (Category.Category.Id A)) | |
203 | 274 ≡⟨ ≡-cong (λ f → f (Category.Category.Id A)) (IsNTrans.commute (isNTrans ha)) ⟩ |
299
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275 TMap ha b (FMap (y-obj A a) g (Category.Category.Id A)) |
195 | 276 ≡⟨⟩ |
277 TMap ha b ( (A Category.o Category.Category.Id A) g ) | |
299
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278 ≡⟨ ≡-cong ( TMap ha b ) ( ≈-≡ {_} {_} {_} {A} (IsCategory.identityL ( Category.isCategory A ))) ⟩ |
195 | 279 TMap ha b g |
280 ∎ | |
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281 )) ⟩ |
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282 TMap ha b |
195 | 283 ∎ |
194 | 284 |
196
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285 -- Yoneda's Lemma |
199 | 286 -- Yoneda Functor is full and faithfull |
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287 -- that is FMapp Yoneda is injective and surjective |
194 | 288 |
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289 -- λ b g → (A Category.o f₁) g |
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290 YondaLemma1 : { c₁ c₂ ℓ : Level} ( A : Category c₁ c₂ ℓ ) {a a' : Obj A } {f : FObj (FObj (YonedaFunctor A) a) a' } |
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291 → SetsAop A [ F2Nat A {a'} {FObj (YonedaFunctor A) a} f ≈ FMap (YonedaFunctor A) f ] |
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292 YondaLemma1 A {a} {a'} {f} = refl |
195 | 293 |
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294 -- F2Nat is bijection so FMap YonedaFunctor also ( using functional extensionality ) |
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295 |
204 | 296 -- Full embedding of Yoneda Functor requires injective on Object, |
297 -- | |
298 -- But we cannot prove like this | |
196
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299 -- FObj YonedaFunctor a ≡ FObj YonedaFunctor b → a ≡ b |
204 | 300 -- YondaLemma2 : {a b x : Obj A } → (FObj (FObj YonedaFunctor a) x) ≡ (FObj (FObj YonedaFunctor b ) x) → |
301 -- a ≡ b | |
302 -- YondaLemma2 {a} {b} eq = {!!} | |
253 | 303 -- N.B = ≡-cong gives you ! a ≡ b, so we cannot cong inv to prove a ≡ b |
204 | 304 -- |
253 | 305 -- Instead we prove only |
204 | 306 -- inv ( FObj YonedaFunctor a ) ≡ a |
196
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307 |
299
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308 inv : { c₁ c₂ ℓ : Level} ( A : Category c₁ c₂ ℓ ) {a x : Obj A} ( f : FObj (FObj (YonedaFunctor A) a) x) → Obj A |
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309 inv A {a} f = Category.cod A f |
203 | 310 |
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311 YonedaLemma21 : { c₁ c₂ ℓ : Level} ( A : Category c₁ c₂ ℓ ) {a x : Obj A} ( f : ( FObj (FObj (YonedaFunctor A ) a) x) ) → inv A f ≡ a |
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312 YonedaLemma21 A {a} {x} f = refl |
203 | 313 |
660 | 314 -- open import Relation.Binary.HeterogeneousEquality |
315 -- | |
316 -- a1 : { c₁ : Level} {A B : Set c₁ } {a : A } { b : B } → a ≅ b → A ≡ B | |
317 -- a1 refl = refl | |
318 -- | |
319 -- YonedaInjective : { c₁ c₂ ℓ : Level} ( A : Category c₁ c₂ ℓ ) {a b : Obj A} | |
320 -- → FObj (YonedaFunctor A ) a ≡ FObj (YonedaFunctor A ) b | |
321 -- → a ≡ b | |
322 -- YonedaInjective A {a} {b} eq = y1 ( ≡-cong ( λ k → FObj k a) eq ) | |
323 -- where | |
324 -- y1 : Hom A a a ≡ Hom A a b → a ≡ b | |
325 -- y1 eq = {!!} | |
326 |