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1 open import Level
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2 open import Category
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3 module CCC where
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4
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5 open import HomReasoning
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6 open import cat-utility
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7 open import Relation.Binary.PropositionalEquality
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8
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9
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10 open import HomReasoning
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11
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12 record IsCCC {c₁ c₂ ℓ : Level} (A : Category c₁ c₂ ℓ)
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13 ( １ : Obj A )
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14 ( ○ : (a : Obj A ) → Hom A a １ )
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15 ( _∧_ : Obj A → Obj A → Obj A )
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16 ( <_,_> : {a b c : Obj A } → Hom A c a → Hom A c b → Hom A c (a ∧ b) )
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17 ( π : {a b : Obj A } → Hom A (a ∧ b) a )
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18 ( π' : {a b : Obj A } → Hom A (a ∧ b) b )
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19 ( _<=_ : (a b : Obj A ) → Obj A )
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20 ( _* : {a b c : Obj A } → Hom A (a ∧ b) c → Hom A a (c <= b) )
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21 ( ε : {a b : Obj A } → Hom A ((a <= b ) ∧ b) a )
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22 : Set ( c₁ ⊔ c₂ ⊔ ℓ ) where
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23 field
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24 -- cartesian
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25 e2 : {a : Obj A} → ∀ ( f : Hom A a １ ) → A [ f ≈ ○ a ]
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26 e3a : {a b c : Obj A} → { f : Hom A c a }{ g : Hom A c b } → A [ A [ π o < f , g > ] ≈ f ]
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27 e3b : {a b c : Obj A} → { f : Hom A c a }{ g : Hom A c b } → A [ A [ π' o < f , g > ] ≈ g ]
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28 e3c : {a b c : Obj A} → { h : Hom A c (a ∧ b) } → A [ < A [ π o h ] , A [ π' o h ] > ≈ h ]
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29 π-cong : {a b c : Obj A} → { f f' : Hom A c a }{ g g' : Hom A c b } → A [ f ≈ f' ] → A [ g ≈ g' ] → A [ < f , g > ≈ < f' , g' > ]
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30 -- closed
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31 e4a : {a b c : Obj A} → { h : Hom A (c ∧ b) a } → A [ A [ ε o < A [ (h *) o π ] , π' > ] ≈ h ]
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32 e4b : {a b c : Obj A} → { k : Hom A c (a <= b ) } → A [ ( A [ ε o < A [ k o π ] , π' > ] ) * ≈ k ]
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33
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34 e'2 : A [ ○ １ ≈ id1 A １ ]
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35 e'2 = let open ≈-Reasoning A in begin
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36 ○ １
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37 ≈↑⟨ e2 (id1 A １ ) ⟩
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38 id1 A １
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39 ∎
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40 e''2 : {a b : Obj A} {f : Hom A a b } → A [ A [ ○ b o f ] ≈ ○ a ]
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41 e''2 {a} {b} {f} = let open ≈-Reasoning A in begin
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42 ○ b o f
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43 ≈⟨ e2 (○ b o f) ⟩
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44 ○ a
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45 ∎
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46 distr : {a b c d : Obj A} {f : Hom A c a }{g : Hom A c b } {h : Hom A d c } → A [ A [ < f , g > o h ] ≈ < A [ f o h ] , A [ g o h ] > ]
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47 distr {a} {b} {c} {d} {f} {g} {h} = let open ≈-Reasoning A in begin
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48 < f , g > o h
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49 ≈↑⟨ e3c ⟩
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50 < π o < f , g > o h , π' o < f , g > o h >
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51 ≈⟨ π-cong assoc assoc ⟩
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52 < ( π o < f , g > ) o h , (π' o < f , g > ) o h >
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53 ≈⟨ π-cong (car e3a ) (car e3b) ⟩
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54 < f o h , g o h >
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55 ∎
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56 _×_ : { a b c d e : Obj A } ( f : Hom A a d ) (g : Hom A b e ) ( h : Hom A c (a ∧ b) ) → Hom A c ( d ∧ e )
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57 f × g = λ h → < A [ f o A [ π o h ] ] , A [ g o A [ π' o h ] ] >
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58
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59 record CCC {c₁ c₂ ℓ : Level} (A : Category c₁ c₂ ℓ) : Set ( c₁ ⊔ c₂ ⊔ ℓ ) where
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60 field
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61 １ : Obj A
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62 ○ : (a : Obj A ) → Hom A a １
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63 _∧_ : Obj A → Obj A → Obj A
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64 <_,_> : {a b c : Obj A } → Hom A c a → Hom A c b → Hom A c (a ∧ b)
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65 π : {a b : Obj A } → Hom A (a ∧ b) a
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66 π' : {a b : Obj A } → Hom A (a ∧ b) b
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67 _<=_ : (a b : Obj A ) → Obj A
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68 _* : {a b c : Obj A } → Hom A (a ∧ b) c → Hom A a (c <= b)
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69 ε : {a b : Obj A } → Hom A ((a <= b ) ∧ b) a
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70 isCCC : IsCCC A １ ○ _∧_ <_,_> π π' _<=_ _* ε
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71
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72
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73
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75
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