feat(library/hott) add the proof that the inverse of an equivalence is an equivalence
This is done by changing the order of theorems and using the adjointification.
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Jakob von Raumer
Leonardo de Moura
parent
e7aa5f65e7
commit
b575c972bd
1 changed files with 52 additions and 46 deletions
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@ -123,76 +123,14 @@ namespace IsEquiv
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... ≈ ap f' ((ap invf ff'a)⁻¹ ⬝ secta) : !ap_pp⁻¹,
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eq3) in
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IsEquiv_mk (inv Hf) sect' retr' adj'
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--TODO: Maybe wait until rewrite rules are available.
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definition inv_closed (Hf : IsEquiv f) : (IsEquiv (inv Hf)) :=
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sorry -- IsEquiv_mk sorry sorry sorry sorry
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definition cancel_R (Hf : IsEquiv f) (Hgf : IsEquiv (g ∘ f)) : (IsEquiv g) :=
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homotopic (comp_closed (inv_closed Hf) Hgf) (λb, ap g (retr Hf b))
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definition cancel_L (Hg : IsEquiv g) (Hgf : IsEquiv (g ∘ f)) : (IsEquiv f) :=
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homotopic (comp_closed Hgf (inv_closed Hg)) (λa, sect Hg (f a))
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definition transport (P : A → Type) {x y : A} (p : x ≈ y) : (IsEquiv (transport P p)) :=
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IsEquiv_mk (transport P (p⁻¹)) (transport_pV P p) (transport_Vp P p) (transport_pVp P p)
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--Rewrite rules
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section
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variables {Hf : IsEquiv f}
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definition moveR_M {x : A} {y : B} (p : x ≈ (inv Hf) y) : (f x ≈ y) :=
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(ap f p) ⬝ (retr Hf y)
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definition moveL_M {x : A} {y : B} (p : (inv Hf) y ≈ x) : (y ≈ f x) :=
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(moveR_M (p⁻¹))⁻¹
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definition moveR_V {x : B} {y : A} (p : x ≈ f y) : (inv Hf) x ≈ y :=
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ap (inv Hf) p ⬝ sect Hf y
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definition moveL_V {x : B} {y : A} (p : f y ≈ x) : y ≈ (inv Hf) x :=
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(moveR_V (p⁻¹))⁻¹
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end
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end IsEquiv
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namespace Equiv
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variables {A B C : Type} (eqf : A ≃ B)
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theorem id : A ≃ A := Equiv_mk id IsEquiv.id_closed
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theorem compose (eqg: B ≃ C) : A ≃ C :=
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Equiv_mk ((equiv_fun eqg) ∘ (equiv_fun eqf))
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(IsEquiv.comp_closed (equiv_isequiv eqf) (equiv_isequiv eqg))
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check IsEquiv.path_closed
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theorem path_closed (f' : A → B) (Heq : equiv_fun eqf ≈ f') : A ≃ B :=
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Equiv_mk f' (IsEquiv.path_closed (equiv_isequiv eqf) Heq)
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theorem inv_closed : B ≃ A :=
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Equiv_mk (IsEquiv.inv (equiv_isequiv eqf)) (IsEquiv.inv_closed (equiv_isequiv eqf))
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theorem cancel_L {f : A → B} {g : B → C}
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(Hf : IsEquiv f) (Hgf : IsEquiv (g ∘ f)) : B ≃ C :=
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Equiv_mk g (IsEquiv.cancel_R _ _)
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theorem cancel_R {f : A → B} {g : B → C}
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(Hg : IsEquiv g) (Hgf : IsEquiv (g ∘ f)) : A ≃ B :=
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Equiv_mk f (!IsEquiv.cancel_L _ _)
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theorem transport (P : A → Type) {x y : A} {p : x ≈ y} : (P x) ≃ (P y) :=
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Equiv_mk (transport P p) (IsEquiv.transport P p)
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end Equiv
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namespace IsEquiv
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variables {A B : Type} (f : A → B) (g : B → A)
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(retr : Sect g f) (sect : Sect f g)
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--To construct an equivalence it suffices to state the proof that the inverse is a quasi-inverse.
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definition adjointify : IsEquiv f :=
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let sect' := (λx, ap g (ap f ((sect x)⁻¹)) ⬝ ap g (retr (f x)) ⬝ sect x) in
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let adj' := (λ (a : A),
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@ -225,5 +163,73 @@ definition adjointify : IsEquiv f :=
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from moveR_M1 _ _ eq3,
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eq4) in
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IsEquiv_mk g retr sect' adj'
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end IsEquiv
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namespace IsEquiv
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variables {A B: Type} {f : A → B} (Hf : IsEquiv f)
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--The inverse of an equivalence is, again, an equivalence.
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definition inv_closed : (IsEquiv (inv Hf)) :=
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adjointify (inv Hf) f (sect Hf) (retr Hf)
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end IsEquiv
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namespace IsEquiv
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variables {A B C : Type} {f : A → B} {g : B → C} {f' : A → B}
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definition cancel_R (Hf : IsEquiv f) (Hgf : IsEquiv (g ∘ f)) : (IsEquiv g) :=
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homotopic (comp_closed (inv_closed Hf) Hgf) (λb, ap g (retr Hf b))
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definition cancel_L (Hg : IsEquiv g) (Hgf : IsEquiv (g ∘ f)) : (IsEquiv f) :=
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homotopic (comp_closed Hgf (inv_closed Hg)) (λa, sect Hg (f a))
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definition transport (P : A → Type) {x y : A} (p : x ≈ y) : (IsEquiv (transport P p)) :=
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IsEquiv_mk (transport P (p⁻¹)) (transport_pV P p) (transport_Vp P p) (transport_pVp P p)
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--Rewrite rules
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section
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variables {Hf : IsEquiv f}
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definition moveR_M {x : A} {y : B} (p : x ≈ (inv Hf) y) : (f x ≈ y) :=
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(ap f p) ⬝ (retr Hf y)
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definition moveL_M {x : A} {y : B} (p : (inv Hf) y ≈ x) : (y ≈ f x) :=
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(moveR_M (p⁻¹))⁻¹
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definition moveR_V {x : B} {y : A} (p : x ≈ f y) : (inv Hf) x ≈ y :=
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ap (inv Hf) p ⬝ sect Hf y
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definition moveL_V {x : B} {y : A} (p : f y ≈ x) : y ≈ (inv Hf) x :=
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(moveR_V (p⁻¹))⁻¹
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end
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end IsEquiv
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namespace Equiv
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variables {A B C : Type} (eqf : A ≃ B)
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theorem id : A ≃ A := Equiv_mk id IsEquiv.id_closed
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theorem compose (eqg: B ≃ C) : A ≃ C :=
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Equiv_mk ((equiv_fun eqg) ∘ (equiv_fun eqf))
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(IsEquiv.comp_closed (equiv_isequiv eqf) (equiv_isequiv eqg))
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theorem path_closed (f' : A → B) (Heq : equiv_fun eqf ≈ f') : A ≃ B :=
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Equiv_mk f' (IsEquiv.path_closed (equiv_isequiv eqf) Heq)
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theorem inv_closed : B ≃ A :=
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Equiv_mk (IsEquiv.inv (equiv_isequiv eqf)) (IsEquiv.inv_closed (equiv_isequiv eqf))
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theorem cancel_L {f : A → B} {g : B → C}
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(Hf : IsEquiv f) (Hgf : IsEquiv (g ∘ f)) : B ≃ C :=
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Equiv_mk g (IsEquiv.cancel_R _ _)
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theorem cancel_R {f : A → B} {g : B → C}
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(Hg : IsEquiv g) (Hgf : IsEquiv (g ∘ f)) : A ≃ B :=
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Equiv_mk f (!IsEquiv.cancel_L _ _)
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theorem transport (P : A → Type) {x y : A} {p : x ≈ y} : (P x) ≃ (P y) :=
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Equiv_mk (transport P p) (IsEquiv.transport P p)
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end Equiv
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