{-# OPTIONS --without-K --safe #-}
module Data.List.Relation.Unary.Any.Properties where
open import Data.Bool.Base using (Bool; false; true; T)
open import Data.Bool.Properties using (T-∨; T-≡)
open import Data.Empty using (⊥)
open import Data.Fin.Base using (Fin; zero; suc)
open import Data.List.Base as List
open import Data.List.Properties using (ʳ++-defn)
open import Data.List.Effectful using (monad)
open import Data.List.Relation.Unary.Any as Any using (Any; here; there)
open import Data.List.Membership.Propositional
open import Data.List.Membership.Propositional.Properties.Core
  using (Any↔; find∘map; map∘find; lose∘find)
open import Data.List.Relation.Binary.Pointwise
  using (Pointwise; []; _∷_)
open import Data.Nat using (zero; suc; _<_; z<s; s<s; s≤s)
open import Data.Nat.Properties using (_≟_; ≤∧≢⇒<; ≤-refl; ≤-step)
open import Data.Maybe.Base using (Maybe; just; nothing)
open import Data.Maybe.Relation.Unary.Any as MAny using (just)
open import Data.Product as Prod
  using (_×_; _,_; ∃; ∃₂; proj₁; proj₂; uncurry′)
open import Data.Product.Properties
open import Data.Product.Function.NonDependent.Propositional
  using (_×-cong_)
import Data.Product.Function.Dependent.Propositional as Σ
open import Data.Sum.Base as Sum using (_⊎_; inj₁; inj₂; [_,_]′)
open import Data.Sum.Function.Propositional using (_⊎-cong_)
open import Effect.Monad
open import Function.Base
open import Function.Equality using (_⟨$⟩_)
open import Function.Equivalence using (_⇔_; equivalence; Equivalence)
open import Function.Inverse as Inv using (_↔_; inverse; Inverse)
open import Function.Related as Related using (Kind; Related; SK-sym)
open import Level using (Level)
open import Relation.Binary as B hiding (_⇔_)
open import Relation.Binary.PropositionalEquality as P
  using (_≡_; refl; inspect)
open import Relation.Unary as U
  using (Pred; _⟨×⟩_; _⟨→⟩_) renaming (_⊆_ to _⋐_)
open import Relation.Nullary using (¬_; _because_; does; ofʸ; ofⁿ; yes; no)
open import Relation.Nullary.Negation using (contradiction; ¬?; decidable-stable)
private
  open module ListMonad {ℓ} = RawMonad (monad {ℓ = ℓ})
private
  variable
    a b c p q r ℓ : Level
    A : Set a
    B : Set b
    C : Set c
    P Q R : Pred A p
    x y : A
    xs ys : List A
lift-resp : ∀ {_≈_ : Rel A ℓ} → P Respects _≈_ →
            (Any P) Respects (Pointwise _≈_)
lift-resp resp (x≈y ∷ xs≈ys) (here px)   = here (resp x≈y px)
lift-resp resp (x≈y ∷ xs≈ys) (there pxs) = there (lift-resp resp xs≈ys pxs)
here-injective : ∀ {p q : P x} → here {P = P} {xs = xs} p ≡ here q → p ≡ q
here-injective refl = refl
there-injective : ∀ {p q : Any P xs} → there {x = x} p ≡ there q → p ≡ q
there-injective refl = refl
¬Any[] : ¬ Any P []
¬Any[] ()
Any-cong : ∀ {k : Kind} → (∀ x → Related k (P x) (Q x)) →
           (∀ {z} → Related k (z ∈ xs) (z ∈ ys)) →
           Related k (Any P xs) (Any Q ys)
Any-cong {P = P} {Q = Q} {xs = xs} {ys} P↔Q xs≈ys =
  Any P xs                ↔⟨ SK-sym Any↔ ⟩
  (∃ λ x → x ∈ xs × P x)  ∼⟨ Σ.cong Inv.id (xs≈ys ×-cong P↔Q _) ⟩
  (∃ λ x → x ∈ ys × Q x)  ↔⟨ Any↔ ⟩
  Any Q ys                ∎
  where open Related.EquationalReasoning
map-id : ∀ (f : P ⋐ P) → (∀ {x} (p : P x) → f p ≡ p) →
         (p : Any P xs) → Any.map f p ≡ p
map-id f hyp (here  p) = P.cong here (hyp p)
map-id f hyp (there p) = P.cong there $ map-id f hyp p
map-∘ : ∀ (f : Q ⋐ R) (g : P ⋐ Q) (p : Any P xs) →
        Any.map (f ∘ g) p ≡ Any.map f (Any.map g p)
map-∘ f g (here  p) = refl
map-∘ f g (there p) = P.cong there $ map-∘ f g p
lookup-result : ∀ (p : Any P xs) → P (Any.lookup p)
lookup-result (here px) = px
lookup-result (there p) = lookup-result p
lookup-index : ∀ (p : Any P xs) → P (lookup xs (Any.index p))
lookup-index (here px)   = px
lookup-index (there pxs) = lookup-index pxs
swap : ∀ {P : A → B → Set ℓ} →
       Any (λ x → Any (P x) ys) xs → Any (λ y → Any (flip P y) xs) ys
swap (here  pys)  = Any.map here pys
swap (there pxys) = Any.map there (swap pxys)
swap-there : ∀ {P : A → B → Set ℓ} →
             (any : Any (λ x → Any (P x) ys) xs) →
             swap (Any.map (there {x = x}) any) ≡ there (swap any)
swap-there (here  pys)  = refl
swap-there (there pxys) = P.cong (Any.map there) (swap-there pxys)
swap-invol : ∀ {P : A → B → Set ℓ} →
             (any : Any (λ x → Any (P x) ys) xs) →
             swap (swap any) ≡ any
swap-invol (here (here px))   = refl
swap-invol (here (there pys)) =
  P.cong (Any.map there) (swap-invol (here pys))
swap-invol (there pxys)       =
  P.trans (swap-there (swap pxys)) (P.cong there (swap-invol pxys))
swap↔ : ∀ {P : A → B → Set ℓ} →
       Any (λ x → Any (P x) ys) xs ↔ Any (λ y → Any (flip P y) xs) ys
swap↔ = inverse swap swap swap-invol swap-invol
⊥↔Any⊥ : ⊥ ↔ Any (const ⊥) xs
⊥↔Any⊥ = inverse (λ()) (λ p → from p) (λ()) (λ p → from p)
  where
  from : Any (const ⊥) xs → B
  from (there p) = from p
⊥↔Any[] : ⊥ ↔ Any P []
⊥↔Any[] = inverse (λ()) (λ()) (λ()) (λ())
any⁺ : ∀ (p : A → Bool) → Any (T ∘ p) xs → T (any p xs)
any⁺ p (here  px)          = Equivalence.from T-∨ ⟨$⟩ inj₁ px
any⁺ p (there {x = x} pxs) with p x
... | true  = _
... | false = any⁺ p pxs
any⁻ : ∀ (p : A → Bool) xs → T (any p xs) → Any (T ∘ p) xs
any⁻ p (x ∷ xs) px∷xs with p x | inspect p x
... | true  | P.[ eq ] = here (Equivalence.from T-≡ ⟨$⟩ eq)
... | false | _        = there (any⁻ p xs px∷xs)
any⇔ : ∀ {p : A → Bool} → Any (T ∘ p) xs ⇔ T (any p xs)
any⇔ = equivalence (any⁺ _) (any⁻ _ _)
Any-⊎⁺ : Any P xs ⊎ Any Q xs → Any (λ x → P x ⊎ Q x) xs
Any-⊎⁺ = [ Any.map inj₁ , Any.map inj₂ ]′
Any-⊎⁻ : Any (λ x → P x ⊎ Q x) xs → Any P xs ⊎ Any Q xs
Any-⊎⁻ (here (inj₁ p)) = inj₁ (here p)
Any-⊎⁻ (here (inj₂ q)) = inj₂ (here q)
Any-⊎⁻ (there p)       = Sum.map there there (Any-⊎⁻ p)
⊎↔ : (Any P xs ⊎ Any Q xs) ↔ Any (λ x → P x ⊎ Q x) xs
⊎↔ {P = P} {Q = Q} = inverse Any-⊎⁺ Any-⊎⁻ from∘to to∘from
  where
  from∘to : (p : Any P xs ⊎ Any Q xs) → Any-⊎⁻ (Any-⊎⁺ p) ≡ p
  from∘to (inj₁ (here  p)) = refl
  from∘to (inj₁ (there p)) rewrite from∘to (inj₁ p) = refl
  from∘to (inj₂ (here  q)) = refl
  from∘to (inj₂ (there q)) rewrite from∘to (inj₂ q) = refl
  to∘from : (p : Any (λ x → P x ⊎ Q x) xs) → Any-⊎⁺ (Any-⊎⁻ p) ≡ p
  to∘from (here (inj₁ p)) = refl
  to∘from (here (inj₂ q)) = refl
  to∘from (there p) with Any-⊎⁻ p | to∘from p
  to∘from (there .(Any.map inj₁ p)) | inj₁ p | refl = refl
  to∘from (there .(Any.map inj₂ q)) | inj₂ q | refl = refl
Any-×⁺ : Any P xs × Any Q ys → Any (λ x → Any (λ y → P x × Q y) ys) xs
Any-×⁺ (p , q) = Any.map (λ p → Any.map (λ q → (p , q)) q) p
Any-×⁻ : Any (λ x → Any (λ y → P x × Q y) ys) xs →
         Any P xs × Any Q ys
Any-×⁻ pq with Prod.map₂ (Prod.map₂ find) (find pq)
... | (x , x∈xs , y , y∈ys , p , q) = lose x∈xs p , lose y∈ys q
×↔ : ∀ {xs ys} →
     (Any P xs × Any Q ys) ↔ Any (λ x → Any (λ y → P x × Q y) ys) xs
×↔ {P = P} {Q = Q} {xs} {ys} = inverse Any-×⁺ Any-×⁻ from∘to to∘from
  where
  open P.≡-Reasoning
  from∘to : ∀ pq → Any-×⁻ (Any-×⁺ pq) ≡ pq
  from∘to (p , q) =
    Any-×⁻ (Any-×⁺ (p , q))
      ≡⟨⟩
    (let (x , x∈xs , pq)    = find (Any-×⁺ (p , q))
         (y , y∈ys , p , q) = find pq
     in  lose x∈xs p , lose y∈ys q)
     ≡⟨ P.cong (λ • → let (x , x∈xs , pq)    = •
                          (y , y∈ys , p , q) = find pq
                      in  lose x∈xs p , lose y∈ys q)
               (find∘map p (λ p → Any.map (p ,_) q)) ⟩
    (let (x , x∈xs , p)     = find p
         (y , y∈ys , p , q) = find (Any.map (p ,_) q)
     in  lose x∈xs p , lose y∈ys q)
     ≡⟨ P.cong (λ • → let (x , x∈xs , p)     = find p
                          (y , y∈ys , p , q) = •
                      in  lose x∈xs p , lose y∈ys q)
               (find∘map q (proj₂ (proj₂ (find p)) ,_)) ⟩
    (let (x , x∈xs , p) = find p
         (y , y∈ys , q) = find q
     in  lose x∈xs p , lose y∈ys q)
     ≡⟨ P.cong₂ _,_ (lose∘find p) (lose∘find q) ⟩
    (p , q) ∎
  to∘from : ∀ pq → Any-×⁺ {xs = xs} (Any-×⁻ pq) ≡ pq
  to∘from pq
    with find pq
      | (λ (f : (proj₁ (find pq) ≡_) ⋐ _) → map∘find pq {f})
  ... | (x , x∈xs , pq′) | lem₁
    with find pq′
      | (λ (f : (proj₁ (find pq′) ≡_) ⋐ _) → map∘find pq′ {f})
  ... | (y , y∈ys , p , q) | lem₂
    rewrite P.sym $ map-∘ {R = λ x → Any (λ y → P x × Q y) ys}
                          (λ p → Any.map (λ q → p , q) (lose y∈ys q))
                          (λ y → P.subst P y p)
                          x∈xs
            = lem₁ _ helper
    where
    helper : Any.map (λ q → p , q) (lose y∈ys q) ≡ pq′
    helper rewrite P.sym $ map-∘ (λ q → p , q)
                                 (λ y → P.subst Q y q)
                                 y∈ys
           = lem₂ _ refl
module _ {_~_ : REL A B r} where
  Any-Σ⁺ʳ : (∃ λ x → Any (_~ x) xs) → Any (∃ ∘ _~_) xs
  Any-Σ⁺ʳ (b , here px) = here (b , px)
  Any-Σ⁺ʳ (b , there pxs) = there (Any-Σ⁺ʳ (b , pxs))
  Any-Σ⁻ʳ : Any (∃ ∘ _~_) xs → ∃ λ x → Any (_~ x) xs
  Any-Σ⁻ʳ (here (b , x)) = b , here x
  Any-Σ⁻ʳ (there xs) = Prod.map₂ there $ Any-Σ⁻ʳ xs
singleton⁺ : P x → Any P [ x ]
singleton⁺ Px = here Px
singleton⁻ : Any P [ x ] → P x
singleton⁻ (here Px) = Px
module _ {f : A → B} where
  map⁺ : Any (P ∘ f) xs → Any P (List.map f xs)
  map⁺ (here p)  = here p
  map⁺ (there p) = there $ map⁺ p
  map⁻ : Any P (List.map f xs) → Any (P ∘ f) xs
  map⁻ {xs = x ∷ xs} (here p)  = here p
  map⁻ {xs = x ∷ xs} (there p) = there $ map⁻ p
  map⁺∘map⁻ : (p : Any P (List.map f xs)) → map⁺ (map⁻ p) ≡ p
  map⁺∘map⁻ {xs = x ∷ xs} (here  p) = refl
  map⁺∘map⁻ {xs = x ∷ xs} (there p) = P.cong there (map⁺∘map⁻ p)
  map⁻∘map⁺ : ∀ (P : Pred B p) →
              (p : Any (P ∘ f) xs) → map⁻ {P = P} (map⁺ p) ≡ p
  map⁻∘map⁺ P (here  p) = refl
  map⁻∘map⁺ P (there p) = P.cong there (map⁻∘map⁺ P p)
  map↔ : Any (P ∘ f) xs ↔ Any P (List.map f xs)
  map↔ = inverse map⁺ map⁻ (map⁻∘map⁺ _) map⁺∘map⁻
  gmap : P ⋐ Q ∘ f → Any P ⋐ Any Q ∘ map f
  gmap g = map⁺ ∘ Any.map g
module _ (f : A → Maybe B) where
  mapMaybe⁺ : ∀ xs → Any (MAny.Any P) (map f xs) → Any P (mapMaybe f xs)
  mapMaybe⁺ (x ∷ xs) ps with f x | ps
  ... | nothing | there pxs      = mapMaybe⁺ xs pxs
  ... | just _  | here (just py) = here py
  ... | just _  | there pxs      = there (mapMaybe⁺ xs pxs)
module _ {P : A → Set p} where
  ++⁺ˡ : Any P xs → Any P (xs ++ ys)
  ++⁺ˡ (here p)  = here p
  ++⁺ˡ (there p) = there (++⁺ˡ p)
  ++⁺ʳ : ∀ xs {ys} → Any P ys → Any P (xs ++ ys)
  ++⁺ʳ []       p = p
  ++⁺ʳ (x ∷ xs) p = there (++⁺ʳ xs p)
  ++⁻ : ∀ xs {ys} → Any P (xs ++ ys) → Any P xs ⊎ Any P ys
  ++⁻ []       p         = inj₂ p
  ++⁻ (x ∷ xs) (here p)  = inj₁ (here p)
  ++⁻ (x ∷ xs) (there p) = Sum.map there id (++⁻ xs p)
  ++⁺∘++⁻ : ∀ xs {ys} (p : Any P (xs ++ ys)) → [ ++⁺ˡ , ++⁺ʳ xs ]′ (++⁻ xs p) ≡ p
  ++⁺∘++⁻ []       p         = refl
  ++⁺∘++⁻ (x ∷ xs) (here  p) = refl
  ++⁺∘++⁻ (x ∷ xs) (there p) with ++⁻ xs p | ++⁺∘++⁻ xs p
  ... | inj₁ p′ | ih = P.cong there ih
  ... | inj₂ p′ | ih = P.cong there ih
  ++⁻∘++⁺ : ∀ xs {ys} (p : Any P xs ⊎ Any P ys) →
            ++⁻ xs ([ ++⁺ˡ , ++⁺ʳ xs ]′ p) ≡ p
  ++⁻∘++⁺ []            (inj₂ p)         = refl
  ++⁻∘++⁺ (x ∷ xs)      (inj₁ (here  p)) = refl
  ++⁻∘++⁺ (x ∷ xs) {ys} (inj₁ (there p)) rewrite ++⁻∘++⁺ xs {ys} (inj₁ p) = refl
  ++⁻∘++⁺ (x ∷ xs)      (inj₂ p)         rewrite ++⁻∘++⁺ xs      (inj₂ p) = refl
  ++↔ : ∀ {xs ys} → (Any P xs ⊎ Any P ys) ↔ Any P (xs ++ ys)
  ++↔ {xs = xs} = inverse [ ++⁺ˡ , ++⁺ʳ xs ]′ (++⁻ xs) (++⁻∘++⁺ xs) (++⁺∘++⁻ xs)
  ++-comm : ∀ xs ys → Any P (xs ++ ys) → Any P (ys ++ xs)
  ++-comm xs ys = [ ++⁺ʳ ys , ++⁺ˡ ]′ ∘ ++⁻ xs
  ++-comm∘++-comm : ∀ xs {ys} (p : Any P (xs ++ ys)) →
                    ++-comm ys xs (++-comm xs ys p) ≡ p
  ++-comm∘++-comm [] {ys} p
    rewrite ++⁻∘++⁺ ys {ys = []} (inj₁ p) = refl
  ++-comm∘++-comm (x ∷ xs) {ys} (here p)
    rewrite ++⁻∘++⁺ ys {ys = x ∷ xs} (inj₂ (here p)) = refl
  ++-comm∘++-comm (x ∷ xs)      (there p) with ++⁻ xs p | ++-comm∘++-comm xs p
  ++-comm∘++-comm (x ∷ xs) {ys} (there .([ ++⁺ʳ xs , ++⁺ˡ ]′ (++⁻ ys (++⁺ʳ ys p))))
    | inj₁ p | refl
    rewrite ++⁻∘++⁺ ys (inj₂                 p)
          | ++⁻∘++⁺ ys (inj₂ $ there {x = x} p) = refl
  ++-comm∘++-comm (x ∷ xs) {ys} (there .([ ++⁺ʳ xs , ++⁺ˡ ]′ (++⁻ ys (++⁺ˡ p))))
    | inj₂ p | refl
    rewrite ++⁻∘++⁺ ys {ys =     xs} (inj₁ p)
          | ++⁻∘++⁺ ys {ys = x ∷ xs} (inj₁ p) = refl
  ++↔++ : ∀ xs ys → Any P (xs ++ ys) ↔ Any P (ys ++ xs)
  ++↔++ xs ys = inverse (++-comm xs ys) (++-comm ys xs)
                        (++-comm∘++-comm xs) (++-comm∘++-comm ys)
  ++-insert : ∀ xs {ys} → P x → Any P (xs ++ [ x ] ++ ys)
  ++-insert xs Px = ++⁺ʳ xs (++⁺ˡ (singleton⁺ Px))
module _ {P : A → Set p} where
  concat⁺ : ∀ {xss} → Any (Any P) xss → Any P (concat xss)
  concat⁺ (here p)           = ++⁺ˡ p
  concat⁺ (there {x = xs} p) = ++⁺ʳ xs (concat⁺ p)
  concat⁻ : ∀ xss → Any P (concat xss) → Any (Any P) xss
  concat⁻ ([]       ∷ xss) p         = there $ concat⁻ xss p
  concat⁻ ((x ∷ xs) ∷ xss) (here  p) = here (here p)
  concat⁻ ((x ∷ xs) ∷ xss) (there p) with concat⁻ (xs ∷ xss) p
  ... | here  p′ = here (there p′)
  ... | there p′ = there p′
  concat⁻∘++⁺ˡ : ∀ {xs} xss (p : Any P xs) →
                 concat⁻ (xs ∷ xss) (++⁺ˡ p) ≡ here p
  concat⁻∘++⁺ˡ xss (here  p) = refl
  concat⁻∘++⁺ˡ xss (there p) rewrite concat⁻∘++⁺ˡ xss p = refl
  concat⁻∘++⁺ʳ : ∀ xs xss (p : Any P (concat xss)) →
                   concat⁻ (xs ∷ xss) (++⁺ʳ xs p) ≡ there (concat⁻ xss p)
  concat⁻∘++⁺ʳ []       xss p = refl
  concat⁻∘++⁺ʳ (x ∷ xs) xss p rewrite concat⁻∘++⁺ʳ xs xss p = refl
  concat⁺∘concat⁻ : ∀ xss (p : Any P (concat xss)) →
                      concat⁺ (concat⁻ xss p) ≡ p
  concat⁺∘concat⁻ ([]       ∷ xss) p         = concat⁺∘concat⁻ xss p
  concat⁺∘concat⁻ ((x ∷ xs) ∷ xss) (here p)  = refl
  concat⁺∘concat⁻ ((x ∷ xs) ∷ xss) (there p)
    with p | concat⁻ (xs ∷ xss) p | concat⁺∘concat⁻ (xs ∷ xss) p
  ... | .(++⁺ˡ p′)              | here  p′ | refl = refl
  ... | .(++⁺ʳ xs (concat⁺ p′)) | there p′ | refl = refl
  concat⁻∘concat⁺ : ∀ {xss} (p : Any (Any P) xss) → concat⁻ xss (concat⁺ p) ≡ p
  concat⁻∘concat⁺ (here                      p) = concat⁻∘++⁺ˡ _ p
  concat⁻∘concat⁺ (there {x = xs} {xs = xss} p)
    rewrite concat⁻∘++⁺ʳ xs xss (concat⁺ p) =
      P.cong there $ concat⁻∘concat⁺ p
  concat↔ : ∀ {xss} → Any (Any P) xss ↔ Any P (concat xss)
  concat↔ {xss} = inverse concat⁺ (concat⁻ xss) concat⁻∘concat⁺ (concat⁺∘concat⁻ xss)
module _ (f : A → B → C) where
  cartesianProductWith⁺ : (∀ {x y} → P x → Q y → R (f x y)) →
                          Any P xs → Any Q ys →
                          Any R (cartesianProductWith f xs ys)
  cartesianProductWith⁺ pres (here  px)  qys = ++⁺ˡ (map⁺ (Any.map (pres px) qys))
  cartesianProductWith⁺ pres (there qxs) qys = ++⁺ʳ _ (cartesianProductWith⁺ pres qxs qys)
  cartesianProductWith⁻ : (∀ {x y} → R (f x y) → P x × Q y) → ∀ xs ys →
                          Any R (cartesianProductWith f xs ys) →
                          Any P xs × Any Q ys
  cartesianProductWith⁻ resp (x ∷ xs) ys Rxsys with ++⁻ (map (f x) ys) Rxsys
  cartesianProductWith⁻ resp (x ∷ xs) ys Rxsys | inj₁ Rfxys with map⁻ Rfxys
  ... | Rxys = here (proj₁ (resp (proj₂ (Any.satisfied Rxys)))) , Any.map (proj₂ ∘ resp) Rxys
  cartesianProductWith⁻ resp (x ∷ xs) ys Rxsys | inj₂ Rc with cartesianProductWith⁻ resp xs ys Rc
  ... | pxs , qys = there pxs , qys
cartesianProduct⁺ : Any P xs → Any Q ys →
                    Any (P ⟨×⟩ Q) (cartesianProduct xs ys)
cartesianProduct⁺ = cartesianProductWith⁺ _,_ _,_
cartesianProduct⁻ : ∀ xs ys → Any (P ⟨×⟩ Q) (cartesianProduct xs ys) →
                    Any P xs × Any Q ys
cartesianProduct⁻ = cartesianProductWith⁻ _,_ id
applyUpTo⁺ : ∀ f {i n} → P (f i) → i < n → Any P (applyUpTo f n)
applyUpTo⁺ _ p z<s       = here p
applyUpTo⁺ f p (s<s i<n@(s≤s _)) =
  there (applyUpTo⁺ (f ∘ suc) p i<n)
applyUpTo⁻ : ∀ f {n} → Any P (applyUpTo f n) →
             ∃ λ i → i < n × P (f i)
applyUpTo⁻ f {suc n} (here p)  = zero , z<s , p
applyUpTo⁻ f {suc n} (there p) with applyUpTo⁻ (f ∘ suc) p
... | i , i<n , q = suc i , s<s i<n , q
module _ {P : A → Set p} where
  applyDownFrom⁺ : ∀ f {i n} → P (f i) → i < n → Any P (applyDownFrom f n)
  applyDownFrom⁺ f {i} {suc n} p (s≤s i≤n) with i ≟ n
  ... | yes P.refl = here p
  ... | no  i≢n    = there (applyDownFrom⁺ f p (≤∧≢⇒< i≤n i≢n))
  applyDownFrom⁻ : ∀ f {n} → Any P (applyDownFrom f n) →
                   ∃ λ i → i < n × P (f i)
  applyDownFrom⁻ f {suc n} (here p)  = n , ≤-refl , p
  applyDownFrom⁻ f {suc n} (there p) with applyDownFrom⁻ f p
  ... | i , i<n , pf = i , ≤-step i<n , pf
tabulate⁺ : ∀ {n} {f : Fin n → A} i → P (f i) → Any P (tabulate f)
tabulate⁺ zero    p = here p
tabulate⁺ (suc i) p = there (tabulate⁺ i p)
tabulate⁻ : ∀ {n} {f : Fin n → A} → Any P (tabulate f) → ∃ λ i → P (f i)
tabulate⁻ {n = suc _} (here p)  = zero , p
tabulate⁻ {n = suc _} (there p) = Prod.map suc id (tabulate⁻ p)
module _ (Q? : U.Decidable Q) where
  filter⁺ : (p : Any P xs) → Any P (filter Q? xs) ⊎ ¬ Q (Any.lookup p)
  filter⁺ {xs = x ∷ _} (here px) with Q? x
  ... | true  because _       = inj₁ (here px)
  ... | false because ofⁿ ¬Qx = inj₂ ¬Qx
  filter⁺ {xs = x ∷ _} (there p) with does (Q? x)
  ... | true  = Sum.map₁ there (filter⁺ p)
  ... | false = filter⁺ p
  filter⁻ : Any P (filter Q? xs) → Any P xs
  filter⁻ {xs = x ∷ xs} p with does (Q? x) | p
  ... | true  | here px   = here px
  ... | true  | there pxs = there (filter⁻ pxs)
  ... | false | pxs       = there (filter⁻ pxs)
module _ {R : A → A → Set r} (R? : B.Decidable R) where
  private
    derun⁺-aux : ∀ x xs → P Respects R → P x → Any P (derun R? (x ∷ xs))
    derun⁺-aux x [] resp Px = here Px
    derun⁺-aux x (y ∷ xs) resp Px with R? x y
    ... | true  because ofʸ Rxy = derun⁺-aux y xs resp (resp Rxy Px)
    ... | false because _       = here Px
  derun⁺ : P Respects R → Any P xs → Any P (derun R? xs)
  derun⁺ {xs = x ∷ xs}     resp (here px)   = derun⁺-aux x xs resp px
  derun⁺ {xs = x ∷ y ∷ xs} resp (there pxs) with does (R? x y)
  ... | true  = derun⁺ resp pxs
  ... | false = there (derun⁺ resp pxs)
  deduplicate⁺ : ∀ {xs} → P Respects (flip R) → Any P xs → Any P (deduplicate R? xs)
  deduplicate⁺ {xs = x ∷ xs} resp (here px)   = here px
  deduplicate⁺ {xs = x ∷ xs} resp (there pxs)
    with filter⁺ (¬? ∘ R? x) (deduplicate⁺ resp pxs)
  ... | inj₁ p = there p
  ... | inj₂ ¬¬q with decidable-stable (R? x (Any.lookup (deduplicate⁺ resp pxs))) ¬¬q
  ...  | q = here (resp q (lookup-result (deduplicate⁺ resp pxs)))
  private
    derun⁻-aux : Any P (derun R? (x ∷ xs)) → Any P (x ∷ xs)
    derun⁻-aux {x = x} {[]}    (here px) = here px
    derun⁻-aux {x = x} {y ∷ _} p[x∷y∷xs] with does (R? x y) | p[x∷y∷xs]
    ... | true  | p[y∷xs]        = there (derun⁻-aux p[y∷xs])
    ... | false | here px        = here px
    ... | false | there p[y∷xs]! = there (derun⁻-aux p[y∷xs]!)
  derun⁻ : Any P (derun R? xs) → Any P xs
  derun⁻ {xs = x ∷ xs} p[x∷xs]! = derun⁻-aux p[x∷xs]!
  deduplicate⁻ : Any P (deduplicate R? xs) → Any P xs
  deduplicate⁻ {xs = x ∷ _} (here px)    = here px
  deduplicate⁻ {xs = x ∷ _} (there pxs!) = there (deduplicate⁻ (filter⁻ (¬? ∘ R? x) pxs!))
module _ {P : B → Set p} where
  mapWith∈⁺ : ∀ {xs : List A} (f : ∀ {x} → x ∈ xs → B) →
                (∃₂ λ x (x∈xs : x ∈ xs) → P (f x∈xs)) →
                Any P (mapWith∈ xs f)
  mapWith∈⁺ f (_ , here refl  , p) = here p
  mapWith∈⁺ f (_ , there x∈xs , p) =
    there $ mapWith∈⁺ (f ∘ there) (_ , x∈xs , p)
  mapWith∈⁻ : ∀ (xs : List A) (f : ∀ {x} → x ∈ xs → B) →
                Any P (mapWith∈ xs f) →
                ∃₂ λ x (x∈xs : x ∈ xs) → P (f x∈xs)
  mapWith∈⁻ (y ∷ xs) f (here  p) = (y , here refl , p)
  mapWith∈⁻ (y ∷ xs) f (there p) =
    Prod.map₂ (Prod.map there id) $ mapWith∈⁻ xs (f ∘ there) p
  mapWith∈↔ : ∀ {xs : List A} {f : ∀ {x} → x ∈ xs → B} →
                (∃₂ λ x (x∈xs : x ∈ xs) → P (f x∈xs)) ↔ Any P (mapWith∈ xs f)
  mapWith∈↔ = inverse (mapWith∈⁺ _) (mapWith∈⁻ _ _) (from∘to _) (to∘from _ _)
    where
    from∘to : ∀ {xs : List A} (f : ∀ {x} → x ∈ xs → B)
              (p : ∃₂ λ x (x∈xs : x ∈ xs) → P (f x∈xs)) →
              mapWith∈⁻ xs f (mapWith∈⁺ f p) ≡ p
    from∘to f (_ , here refl  , p) = refl
    from∘to f (_ , there x∈xs , p)
      rewrite from∘to (f ∘ there) (_ , x∈xs , p) = refl
    to∘from : ∀ (xs : List A) (f : ∀ {x} → x ∈ xs → B)
              (p : Any P (mapWith∈ xs f)) →
              mapWith∈⁺ f (mapWith∈⁻ xs f p) ≡ p
    to∘from (y ∷ xs) f (here  p) = refl
    to∘from (y ∷ xs) f (there p) =
      P.cong there $ to∘from xs (f ∘ there) p
reverseAcc⁺ : ∀ acc xs → Any P acc ⊎ Any P xs → Any P (reverseAcc acc xs)
reverseAcc⁺ acc []       (inj₁ ps)        = ps
reverseAcc⁺ acc (x ∷ xs) (inj₁ ps)        = reverseAcc⁺ (x ∷ acc) xs (inj₁ (there ps))
reverseAcc⁺ acc (x ∷ xs) (inj₂ (here px)) = reverseAcc⁺ (x ∷ acc) xs (inj₁ (here px))
reverseAcc⁺ acc (x ∷ xs) (inj₂ (there y)) = reverseAcc⁺ (x ∷ acc) xs (inj₂ y)
reverseAcc⁻ : ∀ acc xs → Any P (reverseAcc acc xs) → Any P acc ⊎ Any P xs
reverseAcc⁻ acc []       ps = inj₁ ps
reverseAcc⁻ acc (x ∷ xs) ps rewrite ʳ++-defn xs {x ∷ acc} with ++⁻ (reverseAcc [] xs) ps
... | inj₂ (here p') = inj₂ (here p')
... | inj₂ (there ps') = inj₁ ps'
... | inj₁ ps' with reverseAcc⁻ [] xs ps'
...   | inj₂ ps'' = inj₂ (there ps'')
reverse⁺ : Any P xs → Any P (reverse xs)
reverse⁺ ps = reverseAcc⁺ [] _ (inj₂ ps)
reverse⁻ : Any P (reverse xs) → Any P xs
reverse⁻ ps with reverseAcc⁻ [] _ ps
... | inj₂ ps' = ps'
module _ {P : A → Set p} where
  return⁺ : P x → Any P (return x)
  return⁺ = here
  return⁻ : Any P (return x) → P x
  return⁻ (here p) = p
  return⁺∘return⁻ : (p : Any P (return x)) → return⁺ (return⁻ p) ≡ p
  return⁺∘return⁻ (here p) = refl
  return⁻∘return⁺ : (p : P x) → return⁻ (return⁺ p) ≡ p
  return⁻∘return⁺ p = refl
  return↔ : P x ↔ Any P (return x)
  return↔ = inverse return⁺ return⁻ return⁻∘return⁺ return⁺∘return⁻
module _ (P : Pred A p) where
  ∷↔ : (P x ⊎ Any P xs) ↔ Any P (x ∷ xs)
  ∷↔ {x = x} {xs} =
    (P x         ⊎ Any P xs)  ↔⟨ return↔ {P = P} ⊎-cong (Any P xs ∎) ⟩
    (Any P [ x ] ⊎ Any P xs)  ↔⟨ ++↔ {P = P} {xs = [ x ]} ⟩
    Any P (x ∷ xs)            ∎
    where open Related.EquationalReasoning
module _ {A B : Set ℓ} {P : B → Set p} {f : A → List B} where
  >>=↔ : Any (Any P ∘ f) xs ↔ Any P (xs >>= f)
  >>=↔ {xs = xs} =
    Any (Any P ∘ f) xs           ↔⟨ map↔ ⟩
    Any (Any P) (List.map f xs)  ↔⟨ concat↔ ⟩
    Any P (xs >>= f)             ∎
    where open Related.EquationalReasoning
⊛↔ : ∀ {P : B → Set ℓ} {fs : List (A → B)} {xs : List A} →
     Any (λ f → Any (P ∘ f) xs) fs ↔ Any P (fs ⊛ xs)
⊛↔ {P = P} {fs} {xs} =
  Any (λ f → Any (P ∘ f) xs) fs               ↔⟨ Any-cong (λ _ → Any-cong (λ _ → return↔) (_ ∎)) (_ ∎) ⟩
  Any (λ f → Any (Any P ∘ return ∘ f) xs) fs  ↔⟨ Any-cong (λ _ → >>=↔ ) (_ ∎) ⟩
  Any (λ f → Any P (xs >>= return ∘ f)) fs    ↔⟨ >>=↔ ⟩
  Any P (fs ⊛ xs)                             ∎
  where open Related.EquationalReasoning
⊛⁺′ : ∀ {P : A → Set ℓ} {Q : B → Set ℓ} {fs : List (A → B)} {xs} →
      Any (P ⟨→⟩ Q) fs → Any P xs → Any Q (fs ⊛ xs)
⊛⁺′ pq p =
  Inverse.to ⊛↔ ⟨$⟩
    Any.map (λ pq → Any.map (λ {x} → pq {x}) p) pq
⊗↔ : {P : A × B → Set ℓ} {xs : List A} {ys : List B} →
     Any (λ x → Any (λ y → P (x , y)) ys) xs ↔ Any P (xs ⊗ ys)
⊗↔ {P = P} {xs} {ys} =
  Any (λ x → Any (λ y → P (x , y)) ys) xs                             ↔⟨ return↔ ⟩
  Any (λ _,_ → Any (λ x → Any (λ y → P (x , y)) ys) xs) (return _,_)  ↔⟨ ⊛↔ ⟩
  Any (λ x, → Any (P ∘ x,) ys) (_,_ <$> xs)                           ↔⟨ ⊛↔ ⟩
  Any P (xs ⊗ ys)                                                     ∎
  where open Related.EquationalReasoning
⊗↔′ : {P : A → Set ℓ} {Q : B → Set ℓ} {xs : List A} {ys : List B} →
      (Any P xs × Any Q ys) ↔ Any (P ⟨×⟩ Q) (xs ⊗ ys)
⊗↔′ {P = P} {Q} {xs} {ys} =
  (Any P xs × Any Q ys)                    ↔⟨ ×↔ ⟩
  Any (λ x → Any (λ y → P x × Q y) ys) xs  ↔⟨ ⊗↔ ⟩
  Any (P ⟨×⟩ Q) (xs ⊗ ys)                  ∎
  where open Related.EquationalReasoning
map-with-∈⁺ = mapWith∈⁺
{-# WARNING_ON_USAGE map-with-∈⁺
"Warning: map-with-∈⁺ was deprecated in v2.0.
Please use mapWith∈⁺ instead."
#-}
map-with-∈⁻ = mapWith∈⁻
{-# WARNING_ON_USAGE map-with-∈⁻
"Warning: map-with-∈⁻ was deprecated in v2.0.
Please use mapWith∈⁻ instead."
#-}
map-with-∈↔ = mapWith∈↔
{-# WARNING_ON_USAGE map-with-∈↔
"Warning: map-with-∈↔ was deprecated in v2.0.
Please use mapWith∈↔ instead."
#-}