{-# OPTIONS --safe --lossy-unification #-}
module Cubical.Cohomology.EilenbergMacLane.EilenbergSteenrod where
open import Cubical.Homotopy.EilenbergMacLane.GroupStructure
open import Cubical.Homotopy.EilenbergMacLane.Base
open import Cubical.Homotopy.EilenbergMacLane.Properties
open import Cubical.Homotopy.EilenbergSteenrod
open import Cubical.Cohomology.EilenbergMacLane.Base
open import Cubical.Foundations.Prelude
open import Cubical.Foundations.Pointed
open import Cubical.Foundations.Pointed.Homogeneous
open import Cubical.Foundations.GroupoidLaws
open import Cubical.Foundations.Function
open import Cubical.Foundations.Equiv
open import Cubical.Foundations.HLevels
open import Cubical.Foundations.Isomorphism
open import Cubical.Foundations.Univalence
open import Cubical.Algebra.Group
open import Cubical.Algebra.Group.Morphisms
open import Cubical.Algebra.Group.MorphismProperties
open import Cubical.Algebra.AbGroup
open import Cubical.Algebra.AbGroup.Instances.Unit
open import Cubical.Algebra.Group.Instances.Unit
open import Cubical.HITs.Wedge
open import Cubical.HITs.Pushout
open import Cubical.HITs.Susp
open import Cubical.HITs.Truncation as T
open import Cubical.HITs.SetTruncation as ST
open import Cubical.HITs.PropositionalTruncation as PT
open import Cubical.Data.Empty as ⊥
open import Cubical.Data.Nat
open import Cubical.Data.Bool
open import Cubical.Data.Sigma
open import Cubical.Data.Int
open import Cubical.Data.Unit
open Iso
open coHomTheory
coHomRedℤ : ∀ {ℓ ℓ'} → AbGroup ℓ' → ℤ → Pointed ℓ → AbGroup (ℓ-max ℓ ℓ')
coHomRedℤ G (pos n) A = coHomRedGr n G A
coHomRedℤ G (negsuc n) A = UnitAbGroup
module coHomRedℤ {ℓ ℓ'} {G : AbGroup ℓ} where
Hmap∙ : (n : ℤ) {A B : Pointed ℓ'}
→ A →∙ B
→ AbGroupHom (coHomRedℤ G n B) (coHomRedℤ G n A)
Hmap∙ (pos n) = coHomHom∙ n
Hmap∙ (negsuc n) f = idGroupHom
suspMap : (n : ℤ) {A : Pointed ℓ'} →
AbGroupHom (coHomRedℤ G (sucℤ n) (Susp (typ A) , north))
(coHomRedℤ G n A)
fst (suspMap (pos n) {A = A}) =
ST.map λ f → (λ x → ΩEM+1→EM n
(sym (snd f)
∙∙ cong (fst f) (merid x ∙ sym (merid (pt A)))
∙∙ snd f))
, cong (ΩEM+1→EM n)
(cong (sym (snd f) ∙∙_∙∙ snd f)
(cong (cong (fst f))
(rCancel (merid (pt A))))
∙ ∙∙lCancel (snd f))
∙ ΩEM+1→EM-refl n
snd (suspMap (pos n) {A = A}) =
makeIsGroupHom
(ST.elim2 (λ _ _ → isSetPathImplicit)
(λ f g → cong ∣_∣₂ (→∙Homogeneous≡ (isHomogeneousEM n)
(funExt λ x → main n _ (sym (snd f)) _ (sym (snd g))
(cong (fst f) (merid x ∙ sym (merid (pt A))))
(cong (fst g) (merid x ∙ sym (merid (pt A))))))))
where
main : (n : ℕ) (x : EM G (suc n)) (f0 : 0ₖ (suc n) ≡ x)
(y : EM G (suc n)) (g0 : 0ₖ (suc n) ≡ y)
(f1 : x ≡ x) (g1 : y ≡ y)
→ ΩEM+1→EM n (sym (cong₂ _+ₖ_ (sym f0) (sym g0)
∙ rUnitₖ (suc n) (0ₖ (suc n)))
∙∙ cong₂ _+ₖ_ f1 g1
∙∙ (cong₂ _+ₖ_ (sym f0) (sym g0)
∙ rUnitₖ (suc n) (0ₖ (suc n))))
≡ ΩEM+1→EM n (f0 ∙∙ f1 ∙∙ sym f0)
+[ n ]ₖ ΩEM+1→EM n (g0 ∙∙ g1 ∙∙ sym g0)
main zero = J> (J> λ f g →
cong (ΩEM+1→EM {G = G} zero)
(cong (λ x → sym x ∙∙ cong₂ _+ₖ_ f g ∙∙ x)
(sym (rUnit refl))
∙∙ sym (rUnit _)
∙∙ cong₂+₁ f g)
∙∙ ΩEM+1→EM-hom zero f g
∙∙ cong₂ _+ₖ_ (cong (ΩEM+1→EM zero) (rUnit f))
(cong (ΩEM+1→EM zero) (rUnit g)))
main (suc n) =
J> (J> λ f g →
cong (ΩEM+1→EM {G = G} (suc n))
(cong (λ x → sym x ∙∙ cong₂ _+ₖ_ f g ∙∙ x)
(sym (rUnit refl))
∙∙ sym (rUnit _)
∙∙ cong₂+₂ n f g)
∙∙ ΩEM+1→EM-hom (suc n) f g
∙∙ cong₂ _+ₖ_ (cong (ΩEM+1→EM (suc n)) (rUnit f))
(cong (ΩEM+1→EM (suc n)) (rUnit g)))
fst (suspMap (negsuc n)) _ = tt*
snd (suspMap (negsuc n)) = makeIsGroupHom λ _ _ → refl
toSusp-coHomRed : (n : ℕ) {A : Pointed ℓ'}
→ A →∙ EM∙ G n → (Susp (typ A) , north) →∙ EM∙ G (suc n)
fst (toSusp-coHomRed n f) north = 0ₖ (suc n)
fst (toSusp-coHomRed n f) south = 0ₖ (suc n)
fst (toSusp-coHomRed n f) (merid a i) = EM→ΩEM+1 n (fst f a) i
snd (toSusp-coHomRed n f) = refl
suspMapIso : (n : ℤ) {A : Pointed ℓ'} →
AbGroupIso (coHomRedℤ G (sucℤ n) (Susp (typ A) , north))
(coHomRedℤ G n A)
fun (fst (suspMapIso n)) = suspMap n .fst
inv (fst (suspMapIso (pos n))) = ST.map (toSusp-coHomRed n)
inv (fst (suspMapIso (negsuc zero))) _ = 0ₕ∙ zero
inv (fst (suspMapIso (negsuc (suc n)))) _ = tt*
rightInv (fst (suspMapIso (pos n) {A = A})) =
ST.elim (λ _ → isSetPathImplicit)
λ f → cong ∣_∣₂ (→∙Homogeneous≡ (isHomogeneousEM n)
(funExt λ x → cong (ΩEM+1→EM n)
(sym (rUnit _)
∙∙ cong-∙ (toSusp-coHomRed n f .fst)
(merid x) (sym (merid (pt A)))
∙∙ cong (EM→ΩEM+1 n (fst f x) ∙_)
(cong sym (cong (EM→ΩEM+1 n) (snd f)
∙ EM→ΩEM+1-0ₖ n))
∙ sym (rUnit _))
∙ Iso.leftInv (Iso-EM-ΩEM+1 n) (fst f x)))
rightInv (fst (suspMapIso (negsuc zero))) tt* = refl
rightInv (fst (suspMapIso (negsuc (suc n)))) tt* = refl
leftInv (fst (suspMapIso (pos n) {A = A})) =
ST.elim (λ _ → isSetPathImplicit)
λ f → cong ∣_∣₂ (→∙Homogeneous≡ (isHomogeneousEM (suc n))
(funExt λ { north → sym (snd f)
; south → sym (snd f) ∙ cong (fst f) (merid (pt A))
; (merid a i) j → lem a f j i}))
where
lem : (a : typ A) (f : Susp∙ (typ A) →∙ EM∙ G (suc n))
→ PathP (λ i → snd f (~ i) ≡ (sym (snd f) ∙ cong (fst f) (merid (pt A))) i)
(EM→ΩEM+1 n (ΩEM+1→EM n (sym (snd f)
∙∙ cong (fst f) (toSusp A a)
∙∙ snd f)))
(cong (fst f) (merid a))
lem a f = Iso.rightInv (Iso-EM-ΩEM+1 n) _
◁ λ i j → hcomp (λ k
→ λ { (i = i1) → fst f (merid a j)
; (j = i0) → snd f (~ i ∧ k)
; (j = i1) → compPath-filler'
(sym (snd f)) (cong (fst f) (merid (pt A))) k i})
(fst f (compPath-filler (merid a)
(sym (merid (pt A))) (~ i) j))
leftInv (fst (suspMapIso (negsuc zero) {A = A})) =
ST.elim (λ _ → isSetPathImplicit)
λ f → cong ∣_∣₂ (Σ≡Prop (λ _ → hLevelEM G 0 _ _)
(funExt (suspToPropElim (pt A)
(λ _ → hLevelEM G 0 _ _)
(sym (snd f)))))
leftInv (fst (suspMapIso (negsuc (suc n)))) tt* = refl
snd (suspMapIso n) = suspMap n .snd
satisfies-ES : ∀ {ℓ ℓ'} (G : AbGroup ℓ) → coHomTheory {ℓ'} (coHomRedℤ G)
Hmap (satisfies-ES G) = coHomRedℤ.Hmap∙
fst (Suspension (satisfies-ES G)) n = GroupIso→GroupEquiv (coHomRedℤ.suspMapIso n)
snd (Suspension (satisfies-ES G)) f (pos n) =
funExt (ST.elim (λ _ → isSetPathImplicit) λ f
→ cong ∣_∣₂ (→∙Homogeneous≡ (isHomogeneousEM (suc n))
(funExt λ { north → refl
; south → refl
; (merid a i) → refl})))
snd (Suspension (satisfies-ES G)) f (negsuc zero) =
funExt λ {tt* → cong ∣_∣₂ (Σ≡Prop (λ _ → hLevelEM G 0 _ _) refl)}
snd (Suspension (satisfies-ES G)) f (negsuc (suc n)) = refl
Exactness (satisfies-ES G) {A = A} {B = B} f (pos n) = isoToPath help
where
To : (x : coHomRed n G B)
→ isInKer (coHomHom∙ n f) x
→ isInIm (coHomHom∙ n (cfcod (fst f) , refl)) x
To = ST.elim (λ _ → isSetΠ λ _ → isProp→isSet (isPropIsInIm _ _))
λ g p → PT.map (λ id → ∣ (λ { (inl x) → 0ₖ n
; (inr x) → fst g x
; (push a i) → id (~ i) .fst a})
, snd g ∣₂
, cong ∣_∣₂ (→∙Homogeneous≡ (isHomogeneousEM n)
refl))
(Iso.fun ST.PathIdTrunc₀Iso p)
From : (x : coHomRed n G B)
→ isInIm (coHomHom∙ n (cfcod (fst f) , refl)) x
→ isInKer (coHomHom∙ n f) x
From =
ST.elim (λ _ → isSetΠ λ _ → isProp→isSet (isPropIsInKer _ _))
λ g → PT.rec (isPropIsInKer _ _)
(uncurry (ST.elim (λ _ → isSetΠ λ _ → isProp→isSet (isPropIsInKer _ _))
λ h p → PT.rec (squash₂ _ _)
(λ id → cong ∣_∣₂ (→∙Homogeneous≡ (isHomogeneousEM n)
(funExt λ x → sym (funExt⁻ (cong fst id) (fst f x))
∙ cong (fst h) (sym (push x)
∙ push (pt A)
∙ λ i → inr (snd f i))
∙ snd h)))
(Iso.fun ST.PathIdTrunc₀Iso p)))
help : Iso (Ker (coHomHom∙ n f))
(Im (coHomHom∙ n (cfcod (fst f) , refl)))
fun help (x , p) = x , To x p
inv help (x , p) = x , From x p
rightInv help (x , p) = Σ≡Prop (λ _ → isPropIsInIm _ _) refl
leftInv help (x , p) = Σ≡Prop (λ _ → isPropIsInKer _ _) refl
Exactness (satisfies-ES {ℓ} {ℓ'} G) {A = A} {B = B} f (negsuc n) =
isoToPath help
where
help : Iso (Ker (coHomRedℤ.Hmap∙ {G = G} (negsuc n) f))
(Im (coHomRedℤ.Hmap∙ {G = G} (negsuc n) {A = B}
(cfcod (fst f) , refl)))
fun help (tt* , p) = tt* , ∣ tt* , refl ∣₁
inv help (tt* , p) = tt* , refl
rightInv help (tt* , p) = Σ≡Prop (λ _ → isPropIsInIm _ _) refl
leftInv help (tt* , p) = Σ≡Prop (λ _ → isPropIsInKer _ _) refl
Dimension (satisfies-ES G) (pos zero) p = ⊥.rec (p refl)
fst (Dimension (satisfies-ES G) (pos (suc n)) _) = 0ₕ∙ (suc n)
snd (Dimension (satisfies-ES G) (pos (suc n)) _) =
ST.elim (λ _ → isSetPathImplicit)
λ f → T.rec (isProp→isOfHLevelSuc n (squash₂ _ _))
(λ p → cong ∣_∣₂ (→∙Homogeneous≡ (isHomogeneousEM (suc n))
(funExt λ { (lift false) → sym p
; (lift true) → sym (snd f)})))
(Iso.fun (PathIdTruncIso (suc n))
(isContr→isProp (isConnectedEM {G' = G} (suc n))
∣ fst f (lift false) ∣ ∣ 0ₖ (suc n) ∣))
Dimension (satisfies-ES G) (negsuc n) _ = isContrUnit*
BinaryWedge (satisfies-ES G) (pos n) {A = A} {B = B} =
GroupIso→GroupEquiv main
where
main : GroupIso _ _
fun (fst main) =
ST.rec (isSet× squash₂ squash₂)
λ f → ∣ f ∘∙ (inl , refl) ∣₂ , ∣ f ∘∙ (inr , sym (push tt)) ∣₂
inv (fst main) =
uncurry (ST.rec2 squash₂
λ f g → ∣ (λ { (inl x) → fst f x
; (inr x) → fst g x
; (push a i) → (snd f ∙ sym (snd g)) i})
, snd f ∣₂)
rightInv (fst main) =
uncurry
(ST.elim2 (λ _ _ → isOfHLevelPath 2 (isSet× squash₂ squash₂) _ _)
λ f g → ΣPathP
((cong ∣_∣₂ (→∙Homogeneous≡ (isHomogeneousEM n) refl))
, cong ∣_∣₂ (→∙Homogeneous≡ (isHomogeneousEM n) refl)))
leftInv (fst main) =
ST.elim (λ _ → isSetPathImplicit)
λ f → cong ∣_∣₂ (→∙Homogeneous≡ (isHomogeneousEM n)
(funExt λ { (inl x) → refl
; (inr x) → refl
; (push a i) j → lem (snd f) (cong (fst f) (push tt)) j i}))
where
lem : ∀ {ℓ} {A : Type ℓ} {x y z : A}
→ (p : x ≡ y) (q : x ≡ z)
→ (refl ∙ p) ∙ sym (sym q ∙ p) ≡ q
lem p q = cong₂ _∙_ (sym (lUnit p)) (symDistr (sym q) p)
∙ assoc p (sym p) q
∙ cong (_∙ q) (rCancel p)
∙ sym (lUnit q)
snd main =
makeIsGroupHom
(ST.elim2 (λ _ _ → isOfHLevelPath 2 (isSet× squash₂ squash₂) _ _)
λ f g → ΣPathP
(cong ∣_∣₂ (→∙Homogeneous≡ (isHomogeneousEM n) refl)
, (cong ∣_∣₂ (→∙Homogeneous≡ (isHomogeneousEM n) refl))))
BinaryWedge (satisfies-ES G) (negsuc n) {A = A} {B = B} =
invGroupEquiv (GroupIso→GroupEquiv lUnitGroupIso^)