Try to show that natural transformations are sets
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@ -44,7 +44,7 @@ module _ {ℓ ℓ' : Level} (ℂ : Category ℓ ℓ') where
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-- ident-r : concatenate {A} {A} {B} p (lift 𝟙) ≡ p
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-- ident-l : concatenate {A} {B} {B} (lift 𝟙) p ≡ p
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module _ {A B : Object ℂ} where
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isSet : IsSet (Path A B)
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isSet : Cubical.isSet (Path A B)
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isSet = {!!}
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RawFree : RawCategory ℓ (ℓ ⊔ ℓ')
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RawFree = record
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@ -5,6 +5,7 @@ open import Agda.Primitive
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open import Cubical
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open import Function
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open import Data.Product
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import Cubical.GradLemma
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open import Cat.Category
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open import Cat.Category.Functor
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@ -30,6 +31,9 @@ module _ {ℓc ℓc' ℓd ℓd' : Level} {ℂ : Category ℓc ℓc'} {𝔻 : Cat
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→ (f : ℂ [ A , B ])
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→ 𝔻 [ θ B ∘ F.func→ f ] ≡ 𝔻 [ G.func→ f ∘ θ A ]
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-- naturalIsProp : ∀ θ → isProp (Natural θ)
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-- naturalIsProp θ x y = {!funExt!}
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NaturalTransformation : Set (ℓc ⊔ ℓc' ⊔ ℓd')
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NaturalTransformation = Σ Transformation Natural
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@ -90,19 +94,67 @@ module _ {ℓc ℓc' ℓd ℓd' : Level} {ℂ : Category ℓc ℓc'} {𝔻 : Cat
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private
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module _ {F G : Functor ℂ 𝔻} where
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naturalTransformationIsSets : IsSet (NaturalTransformation F G)
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naturalTransformationIsSets {θ , θNat} {η , ηNat} p q i j
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= (λ C → 𝔻.arrowIsSet (λ l → proj₁ (p l) C) (λ l → proj₁ (q l) C) i j)
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, λ f k → 𝔻.arrowIsSet (λ l → proj₂ (p l) f {!!}) (λ l → proj₂ (p l) f {!!}) {!!} {!!}
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where
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module 𝔻 = IsCategory (isCategory 𝔻)
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module _ {A B C D : Functor ℂ 𝔻} {f : NaturalTransformation A B}
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{g : NaturalTransformation B C} {h : NaturalTransformation C D} where
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transformationIsSet : isSet (Transformation F G)
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transformationIsSet _ _ p q i j C = 𝔻.arrowIsSet _ _ (λ l → p l C) (λ l → q l C) i j
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IsSet' : {ℓ : Level} (A : Set ℓ) → Set ℓ
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IsSet' A = {x y : A} → (p q : (λ _ → A) [ x ≡ y ]) → p ≡ q
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-- Example 3.1.6. in HoTT states that
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-- If `B a` is a set for all `a : A` then `(a : A) → B a` is a set.
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-- In the case below `B = Natural F G`.
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-- naturalIsSet : (θ : Transformation F G) → IsSet' (Natural F G θ)
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-- naturalIsSet = {!!}
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-- isS : IsSet' ((θ : Transformation F G) → Natural F G θ)
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-- isS = {!!}
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naturalIsProp : (θ : Transformation F G) → isProp (Natural F G θ)
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naturalIsProp θ θNat θNat' = lem
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where
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lem : (λ _ → Natural F G θ) [ (λ f → θNat f) ≡ (λ f → θNat' f) ]
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lem = λ i f → 𝔻.arrowIsSet _ _ (θNat f) (θNat' f) i
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naturalTransformationIsSets : isSet (NaturalTransformation F G)
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naturalTransformationIsSets (θ , θNat) (η , ηNat) p q i j
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= θ-η
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-- `i or `j - `p'` or `q'`?
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, refl {x = t} i
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-- naturalIsSet i (λ i → {!!} i) {!!} {!!} i j
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-- naturalIsSet {!p''!} {!p''!} {!!} i j
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-- λ f k → 𝔻.arrowIsSet (λ l → proj₂ (p l) f k) (λ l → proj₂ (p l) f k) {!!} {!!}
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where
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θ≡η θ≡η' : θ ≡ η
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θ≡η i = proj₁ (p i)
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θ≡η' i = proj₁ (q i)
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θ-η : Transformation F G
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θ-η = transformationIsSet _ _ θ≡η θ≡η' i j
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θNat≡ηNat : (λ i → Natural F G (θ≡η i)) [ θNat ≡ ηNat ]
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θNat≡ηNat i = proj₂ (p i)
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θNat≡ηNat' : (λ i → Natural F G (θ≡η' i)) [ θNat ≡ ηNat ]
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θNat≡ηNat' i = proj₂ (q i)
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k : Natural F G (θ≡η i)
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k = θNat≡ηNat i
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k' : Natural F G (θ≡η' i)
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k' = θNat≡ηNat' i
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t : Natural F G θ-η
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t = naturalIsProp {!θ!} {!!} {!!} {!!}
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module _ {A B C D : Functor ℂ 𝔻} {θ' : NaturalTransformation A B}
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{η' : NaturalTransformation B C} {ζ' : NaturalTransformation C D} where
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private
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θ = proj₁ θ'
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η = proj₁ η'
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ζ = proj₁ ζ'
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_g⊕f_ = _:⊕:_ {A} {B} {C}
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_h⊕g_ = _:⊕:_ {B} {C} {D}
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:assoc: : (_:⊕:_ {A} {C} {D} h (_:⊕:_ {A} {B} {C} g f)) ≡ (_:⊕:_ {A} {B} {D} (_:⊕:_ {B} {C} {D} h g) f)
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:assoc: = Σ≡ (funExt λ x → {!Fun.arrowIsSet!}) {!!}
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:assoc: : (_:⊕:_ {A} {C} {D} ζ' (_:⊕:_ {A} {B} {C} η' θ')) ≡ (_:⊕:_ {A} {B} {D} (_:⊕:_ {B} {C} {D} ζ' η') θ')
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:assoc: = Σ≡ (funExt (λ _ → assoc)) {!!}
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where
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open IsCategory (isCategory 𝔻)
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module _ {A B : Functor ℂ 𝔻} {f : NaturalTransformation A B} where
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ident-r : (_:⊕:_ {A} {A} {B} f (identityNat A)) ≡ f
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ident-r = {!!}
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@ -11,7 +11,7 @@ open import Data.Product renaming
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)
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open import Data.Empty
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import Function
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open import Cubical hiding (isSet)
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open import Cubical
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open import Cubical.GradLemma using ( propIsEquiv )
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∃! : ∀ {a b} {A : Set a}
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@ -23,12 +23,9 @@ open import Cubical.GradLemma using ( propIsEquiv )
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syntax ∃!-syntax (λ x → B) = ∃![ x ] B
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IsSet : {ℓ : Level} (A : Set ℓ) → Set ℓ
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IsSet A = {x y : A} → (p q : x ≡ y) → p ≡ q
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-- This follows from [HoTT-book: §7.1.10]
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-- Andrea says the proof is in `cubical` but I can't find it.
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postulate isSetIsProp : {ℓ : Level} → {A : Set ℓ} → isProp (IsSet A)
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postulate isSetIsProp : {ℓ : Level} → {A : Set ℓ} → isProp (isSet A)
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record RawCategory (ℓ ℓ' : Level) : Set (lsuc (ℓ' ⊔ ℓ)) where
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-- adding no-eta-equality can speed up type-checking.
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@ -63,7 +60,7 @@ record IsCategory {ℓa ℓb : Level} (ℂ : RawCategory ℓa ℓb) : Set (lsuc
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→ h ∘ (g ∘ f) ≡ (h ∘ g) ∘ f
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ident : {A B : Object} {f : Arrow A B}
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→ f ∘ 𝟙 ≡ f × 𝟙 ∘ f ≡ f
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arrowIsSet : ∀ {A B : Object} → IsSet (Arrow A B)
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arrowIsSet : ∀ {A B : Object} → isSet (Arrow A B)
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Isomorphism : ∀ {A B} → (f : Arrow A B) → Set ℓb
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Isomorphism {A} {B} f = Σ[ g ∈ Arrow B A ] g ∘ f ≡ 𝟙 × f ∘ g ≡ 𝟙
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@ -97,10 +94,10 @@ module _ {ℓa} {ℓb} {ℂ : RawCategory ℓa ℓb} where
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IsCategory-is-prop : isProp (IsCategory ℂ)
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IsCategory-is-prop x y i = record
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-- Why choose `x`'s `arrowIsSet`?
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{ assoc = x.arrowIsSet x.assoc y.assoc i
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{ assoc = x.arrowIsSet _ _ x.assoc y.assoc i
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; ident =
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( x.arrowIsSet (fst x.ident) (fst y.ident) i
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, x.arrowIsSet (snd x.ident) (snd y.ident) i
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( x.arrowIsSet _ _ (fst x.ident) (fst y.ident) i
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, x.arrowIsSet _ _ (snd x.ident) (snd y.ident) i
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)
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; arrowIsSet = isSetIsProp x.arrowIsSet y.arrowIsSet i
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; univalent = {!!}
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@ -123,8 +120,8 @@ module _ {ℓa} {ℓb} {ℂ : RawCategory ℓa ℓb} where
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(λ f → Σ-syntax (Arrow (A≡B j) A) (λ g → g ∘ f ≡ 𝟙 × f ∘ g ≡ 𝟙)))
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( 𝟙
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, 𝟙
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, x.arrowIsSet (fst x.ident) (fst y.ident) i
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, x.arrowIsSet (snd x.ident) (snd y.ident) i
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, x.arrowIsSet _ _ (fst x.ident) (fst y.ident) i
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, x.arrowIsSet _ _ (snd x.ident) (snd y.ident) i
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)
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)
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eqUni : T [ xuni ≡ yuni ]
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@ -61,14 +61,14 @@ module _
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IsFunctorIsProp : isProp (IsFunctor _ _ F)
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IsFunctorIsProp isF0 isF1 i = record
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{ ident = 𝔻.arrowIsSet isF0.ident isF1.ident i
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; distrib = 𝔻.arrowIsSet isF0.distrib isF1.distrib i
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{ ident = 𝔻.arrowIsSet _ _ isF0.ident isF1.ident i
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; distrib = 𝔻.arrowIsSet _ _ isF0.distrib isF1.distrib i
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}
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where
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module isF0 = IsFunctor isF0
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module isF1 = IsFunctor isF1
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-- Alternate version of above where `F` is a path in
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-- Alternate version of above where `F` is indexed by an interval
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module _
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{ℓa ℓb : Level}
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{ℂ 𝔻 : Category ℓa ℓb}
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@ -1,3 +1,4 @@
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{-# OPTIONS --cubical #-}
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-- Defines equality-principles for data-types from the standard library.
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module Cat.Equality where
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@ -19,3 +20,28 @@ module Equality where
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Σ≡ : a ≡ b
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proj₁ (Σ≡ i) = proj₁≡ i
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proj₂ (Σ≡ i) = proj₂≡ i
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-- Remark 2.7.1: This theorem:
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--
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-- (x , u) ≡ (x , v) → u ≡ v
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--
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-- does *not* hold! We can only conclude that there *exists* `p : x ≡ x`
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-- such that
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--
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-- p* u ≡ v
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-- thm : isSet A → (∀ {a} → isSet (B a)) → isSet (Σ A B)
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-- thm sA sB (x , y) (x' , y') p q = res
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-- where
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-- x≡x'0 : x ≡ x'
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-- x≡x'0 = λ i → proj₁ (p i)
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-- x≡x'1 : x ≡ x'
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-- x≡x'1 = λ i → proj₁ (q i)
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-- someP : x ≡ x'
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-- someP = {!!}
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-- tricky : {!y!} ≡ y'
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-- tricky = {!!}
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-- -- res' : (λ _ → Σ A B) [ (x , y) ≡ (x' , y') ]
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-- res' : ({!!} , {!!}) ≡ ({!!} , {!!})
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-- res' = {!!}
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-- res : p ≡ q
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-- res i = {!res'!}
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