{-# OPTIONS --without-K --safe #-}
module Data.List.Relation.Binary.BagAndSetEquality where
open import Algebra using (Idempotent; CommutativeMonoid)
open import Algebra.Structures.Biased using (isCommutativeMonoidˡ)
open import Category.Monad using (RawMonad)
open import Data.Empty
open import Data.Fin.Base
open import Data.List.Base
open import Data.List.Categorical using (monad; module MonadProperties)
import Data.List.Properties as LP
open import Data.List.Relation.Unary.Any using (Any; here; there)
open import Data.List.Relation.Unary.Any.Properties
open import Data.List.Membership.Propositional using (_∈_)
open import Data.List.Relation.Binary.Subset.Propositional.Properties
using (⊆-preorder)
open import Data.Product as Prod hiding (map)
import Data.Product.Function.Dependent.Propositional as Σ
open import Data.Sum.Base as Sum hiding (map)
open import Data.Sum.Properties
open import Data.Sum.Function.Propositional using (_⊎-cong_)
open import Data.Unit
open import Function.Base
open import Function.Equality using (_⟨$⟩_)
import Function.Equivalence as FE
open import Function.Inverse as Inv using (_↔_; Inverse; inverse)
open import Function.Related as Related
using (↔⇒; ⌊_⌋; ⌊_⌋→; ⇒→; K-refl; SK-sym)
open import Function.Related.TypeIsomorphisms
open import Level using (Lift)
open import Relation.Binary
import Relation.Binary.Reasoning.Setoid as EqR
import Relation.Binary.Reasoning.Preorder as PreorderReasoning
open import Relation.Binary.PropositionalEquality as P
using (_≡_; _≢_; _≗_; refl)
open import Relation.Nullary
open import Data.List.Membership.Propositional.Properties
open Related public using (Kind; Symmetric-kind) renaming
( implication to subset
; reverse-implication to superset
; equivalence to set
; injection to subbag
; reverse-injection to superbag
; bijection to bag
)
[_]-Order : Kind → ∀ {a} → Set a → Preorder _ _ _
[ k ]-Order A = Related.InducedPreorder₂ k {A = A} _∈_
[_]-Equality : Symmetric-kind → ∀ {a} → Set a → Setoid _ _
[ k ]-Equality A = Related.InducedEquivalence₂ k {A = A} _∈_
infix 4 _∼[_]_
_∼[_]_ : ∀ {a} {A : Set a} → List A → Kind → List A → Set _
_∼[_]_ {A = A} xs k ys = Preorder._∼_ ([ k ]-Order A) xs ys
private
module Eq {k a} {A : Set a} = Setoid ([ k ]-Equality A)
module Ord {k a} {A : Set a} = Preorder ([ k ]-Order A)
open module ListMonad {ℓ} = RawMonad (monad {ℓ = ℓ})
module MP = MonadProperties
bag-=⇒ : ∀ {k a} {A : Set a} {xs ys : List A} →
xs ∼[ bag ] ys → xs ∼[ k ] ys
bag-=⇒ xs≈ys = ↔⇒ xs≈ys
module ⊆-Reasoning where
private
module PreOrder {a} {A : Set a} = PreorderReasoning (⊆-preorder A)
open PreOrder public
hiding (step-≈; step-≈˘; step-∼)
infixr 2 step-∼ step-⊆
infix 1 step-∈
step-⊆ = PreOrder.step-∼
step-∈ : ∀ {a} {A : Set a} x {xs ys : List A} →
xs IsRelatedTo ys → x ∈ xs → x ∈ ys
step-∈ x xs⊆ys x∈xs = (begin xs⊆ys) x∈xs
step-∼ : ∀ {k a} {A : Set a} xs {ys zs : List A} →
ys IsRelatedTo zs → xs ∼[ ⌊ k ⌋→ ] ys → xs IsRelatedTo zs
step-∼ xs ys⊆zs xs≈ys = step-⊆ xs ys⊆zs (⇒→ xs≈ys)
syntax step-∈ x xs⊆ys x∈xs = x ∈⟨ x∈xs ⟩ xs⊆ys
syntax step-∼ xs ys⊆zs xs≈ys = xs ∼⟨ xs≈ys ⟩ ys⊆zs
syntax step-⊆ xs ys⊆zs xs⊆ys = xs ⊆⟨ xs⊆ys ⟩ ys⊆zs
module _ {a k} {A : Set a} {x y : A} {xs ys} where
∷-cong : x ≡ y → xs ∼[ k ] ys → x ∷ xs ∼[ k ] y ∷ ys
∷-cong refl xs≈ys {y} =
y ∈ x ∷ xs ↔⟨ SK-sym $ ∷↔ (y ≡_) ⟩
(y ≡ x ⊎ y ∈ xs) ∼⟨ (y ≡ x ∎) ⊎-cong xs≈ys ⟩
(y ≡ x ⊎ y ∈ ys) ↔⟨ ∷↔ (y ≡_) ⟩
y ∈ x ∷ ys ∎
where open Related.EquationalReasoning
module _ {ℓ k} {A B : Set ℓ} {f g : A → B} {xs ys} where
map-cong : f ≗ g → xs ∼[ k ] ys → map f xs ∼[ k ] map g ys
map-cong f≗g xs≈ys {x} =
x ∈ map f xs ↔⟨ SK-sym $ map↔ ⟩
Any (λ y → x ≡ f y) xs ∼⟨ Any-cong (↔⇒ ∘ helper) xs≈ys ⟩
Any (λ y → x ≡ g y) ys ↔⟨ map↔ ⟩
x ∈ map g ys ∎
where
open Related.EquationalReasoning
helper : ∀ y → x ≡ f y ↔ x ≡ g y
helper y = record
{ to = P.→-to-⟶ (λ x≡fy → P.trans x≡fy ( f≗g y))
; from = P.→-to-⟶ (λ x≡gy → P.trans x≡gy (P.sym $ f≗g y))
; inverse-of = record
{ left-inverse-of = λ { P.refl → P.trans-symʳ (f≗g y) }
; right-inverse-of = λ { P.refl → P.trans-symˡ (f≗g y) }
}
}
module _ {a k} {A : Set a} {xs₁ xs₂ ys₁ ys₂ : List A} where
++-cong : xs₁ ∼[ k ] xs₂ → ys₁ ∼[ k ] ys₂ →
xs₁ ++ ys₁ ∼[ k ] xs₂ ++ ys₂
++-cong xs₁≈xs₂ ys₁≈ys₂ {x} =
x ∈ xs₁ ++ ys₁ ↔⟨ SK-sym $ ++↔ ⟩
(x ∈ xs₁ ⊎ x ∈ ys₁) ∼⟨ xs₁≈xs₂ ⊎-cong ys₁≈ys₂ ⟩
(x ∈ xs₂ ⊎ x ∈ ys₂) ↔⟨ ++↔ ⟩
x ∈ xs₂ ++ ys₂ ∎
where open Related.EquationalReasoning
module _ {a k} {A : Set a} {xss yss : List (List A)} where
concat-cong : xss ∼[ k ] yss → concat xss ∼[ k ] concat yss
concat-cong xss≈yss {x} =
x ∈ concat xss ↔⟨ SK-sym concat↔ ⟩
Any (Any (x ≡_)) xss ∼⟨ Any-cong (λ _ → _ ∎) xss≈yss ⟩
Any (Any (x ≡_)) yss ↔⟨ concat↔ ⟩
x ∈ concat yss ∎
where open Related.EquationalReasoning
module _ {ℓ k} {A B : Set ℓ} {xs ys} {f g : A → List B} where
>>=-cong : xs ∼[ k ] ys → (∀ x → f x ∼[ k ] g x) →
(xs >>= f) ∼[ k ] (ys >>= g)
>>=-cong xs≈ys f≈g {x} =
x ∈ (xs >>= f) ↔⟨ SK-sym >>=↔ ⟩
Any (λ y → x ∈ f y) xs ∼⟨ Any-cong (λ x → f≈g x) xs≈ys ⟩
Any (λ y → x ∈ g y) ys ↔⟨ >>=↔ ⟩
x ∈ (ys >>= g) ∎
where open Related.EquationalReasoning
module _ {ℓ k} {A B : Set ℓ} {fs gs : List (A → B)} {xs ys} where
⊛-cong : fs ∼[ k ] gs → xs ∼[ k ] ys → (fs ⊛ xs) ∼[ k ] (gs ⊛ ys)
⊛-cong fs≈gs xs≈ys =
>>=-cong fs≈gs λ f →
>>=-cong xs≈ys λ x →
_ ∎
where open Related.EquationalReasoning
module _ {ℓ k} {A B : Set ℓ} {xs₁ xs₂ : List A} {ys₁ ys₂ : List B} where
⊗-cong : xs₁ ∼[ k ] xs₂ → ys₁ ∼[ k ] ys₂ →
(xs₁ ⊗ ys₁) ∼[ k ] (xs₂ ⊗ ys₂)
⊗-cong xs₁≈xs₂ ys₁≈ys₂ =
⊛-cong (⊛-cong (Ord.refl {x = [ _,_ ]}) xs₁≈xs₂) ys₁≈ys₂
commutativeMonoid : ∀ {a} → Symmetric-kind → Set a →
CommutativeMonoid _ _
commutativeMonoid {a} k A = record
{ Carrier = List A
; _≈_ = _∼[ ⌊ k ⌋ ]_
; _∙_ = _++_
; ε = []
; isCommutativeMonoid = isCommutativeMonoidˡ record
{ isSemigroup = record
{ isMagma = record
{ isEquivalence = Eq.isEquivalence
; ∙-cong = ++-cong
}
; assoc = λ xs ys zs →
Eq.reflexive (LP.++-assoc xs ys zs)
}
; identityˡ = λ xs {x} → x ∈ xs ∎
; comm = λ xs ys {x} →
x ∈ xs ++ ys ↔⟨ ++↔++ xs ys ⟩
x ∈ ys ++ xs ∎
}
}
where open Related.EquationalReasoning
empty-unique : ∀ {k a} {A : Set a} {xs : List A} →
xs ∼[ ⌊ k ⌋→ ] [] → xs ≡ []
empty-unique {xs = []} _ = refl
empty-unique {xs = _ ∷ _} ∷∼[] with ⇒→ ∷∼[] (here refl)
... | ()
++-idempotent : ∀ {a} {A : Set a} → Idempotent {A = List A} _∼[ set ]_ _++_
++-idempotent {a} xs {x} =
x ∈ xs ++ xs ∼⟨ FE.equivalence ([ id , id ]′ ∘ _⟨$⟩_ (Inverse.from $ ++↔))
(_⟨$⟩_ (Inverse.to $ ++↔) ∘ inj₁) ⟩
x ∈ xs ∎
where open Related.EquationalReasoning
>>=-left-distributive :
∀ {ℓ} {A B : Set ℓ} (xs : List A) {f g : A → List B} →
(xs >>= λ x → f x ++ g x) ∼[ bag ] (xs >>= f) ++ (xs >>= g)
>>=-left-distributive {ℓ} xs {f} {g} {y} =
y ∈ (xs >>= λ x → f x ++ g x) ↔⟨ SK-sym $ >>=↔ ⟩
Any (λ x → y ∈ f x ++ g x) xs ↔⟨ SK-sym (Any-cong (λ _ → ++↔) (_ ∎)) ⟩
Any (λ x → y ∈ f x ⊎ y ∈ g x) xs ↔⟨ SK-sym $ ⊎↔ ⟩
(Any (λ x → y ∈ f x) xs ⊎ Any (λ x → y ∈ g x) xs) ↔⟨ >>=↔ ⟨ _⊎-cong_ ⟩ >>=↔ ⟩
(y ∈ (xs >>= f) ⊎ y ∈ (xs >>= g)) ↔⟨ ++↔ ⟩
y ∈ (xs >>= f) ++ (xs >>= g) ∎
where open Related.EquationalReasoning
⊛-left-distributive :
∀ {ℓ} {A B : Set ℓ} (fs : List (A → B)) xs₁ xs₂ →
(fs ⊛ (xs₁ ++ xs₂)) ∼[ bag ] (fs ⊛ xs₁) ++ (fs ⊛ xs₂)
⊛-left-distributive {B = B} fs xs₁ xs₂ = begin
fs ⊛ (xs₁ ++ xs₂) ≡⟨⟩
(fs >>= λ f → xs₁ ++ xs₂ >>= return ∘ f) ≡⟨ (MP.cong (refl {x = fs}) λ f →
MP.right-distributive xs₁ xs₂ (return ∘ f)) ⟩
(fs >>= λ f → (xs₁ >>= return ∘ f) ++
(xs₂ >>= return ∘ f)) ≈⟨ >>=-left-distributive fs ⟩
(fs >>= λ f → xs₁ >>= return ∘ f) ++
(fs >>= λ f → xs₂ >>= return ∘ f) ≡⟨⟩
(fs ⊛ xs₁) ++ (fs ⊛ xs₂) ∎
where open EqR ([ bag ]-Equality B)
private
¬-drop-cons : ∀ {a} {A : Set a} {x : A} →
¬ (∀ {xs ys} → x ∷ xs ∼[ set ] x ∷ ys → xs ∼[ set ] ys)
¬-drop-cons {x = x} drop-cons
with FE.Equivalence.to x∼[] ⟨$⟩ here refl
where
x,x≈x : (x ∷ x ∷ []) ∼[ set ] [ x ]
x,x≈x = ++-idempotent [ x ]
x∼[] : [ x ] ∼[ set ] []
x∼[] = drop-cons x,x≈x
... | ()
drop-cons : ∀ {a} {A : Set a} {x : A} {xs ys} →
x ∷ xs ∼[ bag ] x ∷ ys → xs ∼[ bag ] ys
drop-cons {A = A} {x} {xs} {ys} x∷xs≈x∷ys =
⊎-left-cancellative
(∼→⊎↔⊎ x∷xs≈x∷ys)
(lemma x∷xs≈x∷ys)
(lemma (SK-sym x∷xs≈x∷ys))
where
∈-index : ∀ {a} {A : Set a} {z}
(xs : List A) → z ∈ xs ↔ ∃ λ i → z ≡ lookup xs i
∈-index {z = z} [] =
z ∈ [] ↔⟨ SK-sym ⊥↔Any[] ⟩
⊥ ↔⟨ SK-sym $ inverse (λ { (() , _) }) (λ ()) (λ { (() , _) }) (λ ()) ⟩
(∃ λ (i : Fin 0) → z ≡ lookup [] i) ∎
where
open Related.EquationalReasoning
∈-index {z = z} (x ∷ xs) =
z ∈ x ∷ xs ↔⟨ SK-sym (∷↔ _) ⟩
(z ≡ x ⊎ z ∈ xs) ↔⟨ K-refl ⊎-cong ∈-index xs ⟩
(z ≡ x ⊎ ∃ λ i → z ≡ lookup xs i) ↔⟨ SK-sym $ inverse (λ { (zero , p) → inj₁ p; (suc i , p) → inj₂ (i , p) })
(λ { (inj₁ p) → zero , p; (inj₂ (i , p)) → suc i , p })
(λ { (zero , _) → refl; (suc _ , _) → refl })
(λ { (inj₁ _) → refl; (inj₂ _) → refl }) ⟩
(∃ λ i → z ≡ lookup (x ∷ xs) i) ∎
where
open Related.EquationalReasoning
index-of : ∀ {a} {A : Set a} {z} {xs : List A} →
z ∈ xs → Fin (length xs)
index-of = proj₁ ∘ (Inverse.to (∈-index _) ⟨$⟩_)
Fin-length : ∀ {a} {A : Set a}
(xs : List A) → (∃ λ z → z ∈ xs) ↔ Fin (length xs)
Fin-length xs =
(∃ λ z → z ∈ xs) ↔⟨ Σ.cong K-refl (∈-index xs) ⟩
(∃ λ z → ∃ λ i → z ≡ lookup xs i) ↔⟨ ∃∃↔∃∃ _ ⟩
(∃ λ i → ∃ λ z → z ≡ lookup xs i) ↔⟨ Σ.cong K-refl (inverse _ (λ _ → _ , refl) (λ { (_ , refl) → refl }) (λ _ → refl)) ⟩
(Fin (length xs) × Lift _ ⊤) ↔⟨ ×-identityʳ _ _ ⟩
Fin (length xs) ∎
where
open Related.EquationalReasoning
Fin-length-cong : ∀ {a} {A : Set a} {xs ys : List A} →
xs ∼[ bag ] ys → Fin (length xs) ↔ Fin (length ys)
Fin-length-cong {xs = xs} {ys} xs≈ys =
Fin (length xs) ↔⟨ SK-sym $ Fin-length xs ⟩
∃ (λ z → z ∈ xs) ↔⟨ Σ.cong K-refl xs≈ys ⟩
∃ (λ z → z ∈ ys) ↔⟨ Fin-length ys ⟩
Fin (length ys) ∎
where
open Related.EquationalReasoning
index-of-commutes :
∀ {a} {A : Set a} {z : A} {xs ys} →
(xs≈ys : xs ∼[ bag ] ys) (p : z ∈ xs) →
index-of (Inverse.to xs≈ys ⟨$⟩ p) ≡
Inverse.to (Fin-length-cong xs≈ys) ⟨$⟩ index-of p
index-of-commutes {z = z} {xs} {ys} xs≈ys p =
index-of (to xs≈ys ⟨$⟩ p) ≡⟨ lemma z p ⟩
index-of (to xs≈ys ⟨$⟩ proj₂
(from (Fin-length xs) ⟨$⟩ (to (Fin-length xs) ⟨$⟩ (z , p)))) ≡⟨⟩
index-of (proj₂ (Prod.map id (to xs≈ys ⟨$⟩_)
(from (Fin-length xs) ⟨$⟩ (to (Fin-length xs) ⟨$⟩ (z , p))))) ≡⟨⟩
to (Fin-length ys) ⟨$⟩ Prod.map id (to xs≈ys ⟨$⟩_)
(from (Fin-length xs) ⟨$⟩ index-of p) ≡⟨⟩
to (Fin-length-cong xs≈ys) ⟨$⟩ index-of p ∎
where
open P.≡-Reasoning
open Inverse
lemma :
∀ z p →
index-of (to xs≈ys ⟨$⟩ p) ≡
index-of (to xs≈ys ⟨$⟩ proj₂
(from (Fin-length xs) ⟨$⟩ (to (Fin-length xs) ⟨$⟩ (z , p))))
lemma z p with to (Fin-length xs) ⟨$⟩ (z , p)
| left-inverse-of (Fin-length xs) (z , p)
lemma .(lookup xs i) .(from (∈-index xs) ⟨$⟩ (i , refl)) | i | refl =
refl
index-equality-preserved :
∀ {a} {A : Set a} {z : A} {xs ys} {p q : z ∈ xs}
(xs≈ys : xs ∼[ bag ] ys) →
index-of p ≡ index-of q →
index-of (Inverse.to xs≈ys ⟨$⟩ p) ≡
index-of (Inverse.to xs≈ys ⟨$⟩ q)
index-equality-preserved {p = p} {q} xs≈ys eq =
index-of (Inverse.to xs≈ys ⟨$⟩ p) ≡⟨ index-of-commutes xs≈ys p ⟩
Inverse.to (Fin-length-cong xs≈ys) ⟨$⟩ index-of p ≡⟨ P.cong (Inverse.to (Fin-length-cong xs≈ys) ⟨$⟩_) eq ⟩
Inverse.to (Fin-length-cong xs≈ys) ⟨$⟩ index-of q ≡⟨ P.sym $ index-of-commutes xs≈ys q ⟩
index-of (Inverse.to xs≈ys ⟨$⟩ q) ∎
where
open P.≡-Reasoning
inspect : ∀ {a} {A : Set a} (x : A) → ∃ (x ≡_)
inspect x = x , refl
Well-behaved : ∀ {a b c} {A : Set a} {B : Set b} {C : Set c} →
(A ⊎ B → A ⊎ C) → Set _
Well-behaved f =
∀ {b a a′} → f (inj₂ b) ≡ inj₁ a → f (inj₁ a) ≢ inj₁ a′
⊎-left-cancellative :
∀ {a b c} {A : Set a} {B : Set b} {C : Set c}
(f : (A ⊎ B) ↔ (A ⊎ C)) →
Well-behaved (Inverse.to f ⟨$⟩_) →
Well-behaved (Inverse.from f ⟨$⟩_) →
B ↔ C
⊎-left-cancellative {A = A} = λ inv to-hyp from-hyp → inverse
(g (to inv ⟨$⟩_) to-hyp)
(g (from inv ⟨$⟩_) from-hyp)
(g∘g inv to-hyp from-hyp)
(g∘g (SK-sym inv) from-hyp to-hyp)
where
open Inverse
module _
{a b c} {A : Set a} {B : Set b} {C : Set c}
(f : A ⊎ B → A ⊎ C)
(hyp : Well-behaved f)
where
mutual
g : B → C
g b = g′ (inspect (f (inj₂ b)))
g′ : ∀ {b} → ∃ (f (inj₂ b) ≡_) → C
g′ (inj₂ c , _) = c
g′ (inj₁ a , eq) = g″ eq (inspect (f (inj₁ a)))
g″ : ∀ {a b} →
f (inj₂ b) ≡ inj₁ a → ∃ (f (inj₁ a) ≡_) → C
g″ _ (inj₂ c , _) = c
g″ eq₁ (inj₁ _ , eq₂) = ⊥-elim $ hyp eq₁ eq₂
g∘g : ∀ {b c} {B : Set b} {C : Set c}
(f : (A ⊎ B) ↔ (A ⊎ C)) →
(to-hyp : Well-behaved (to f ⟨$⟩_)) →
(from-hyp : Well-behaved (from f ⟨$⟩_)) →
∀ b → g (from f ⟨$⟩_) from-hyp (g (to f ⟨$⟩_) to-hyp b) ≡ b
g∘g f to-hyp from-hyp b = g∘g′
where
open P.≡-Reasoning
g∘g′ : g (from f ⟨$⟩_) from-hyp (g (to f ⟨$⟩_) to-hyp b) ≡ b
g∘g′ with inspect (to f ⟨$⟩ inj₂ b)
g∘g′ | inj₂ c , eq₁ with inspect (from f ⟨$⟩ inj₂ c)
g∘g′ | inj₂ c , eq₁ | inj₂ b′ , eq₂ = inj₂-injective (
inj₂ b′ ≡⟨ P.sym eq₂ ⟩
from f ⟨$⟩ inj₂ c ≡⟨ to-from f eq₁ ⟩
inj₂ b ∎)
g∘g′ | inj₂ c , eq₁ | inj₁ a , eq₂ with
inj₁ a ≡⟨ P.sym eq₂ ⟩
from f ⟨$⟩ inj₂ c ≡⟨ to-from f eq₁ ⟩
inj₂ b ∎
... | ()
g∘g′ | inj₁ a , eq₁ with inspect (to f ⟨$⟩ inj₁ a)
g∘g′ | inj₁ a , eq₁ | inj₁ a′ , eq₂ = ⊥-elim $ to-hyp eq₁ eq₂
g∘g′ | inj₁ a , eq₁ | inj₂ c , eq₂ with inspect (from f ⟨$⟩ inj₂ c)
g∘g′ | inj₁ a , eq₁ | inj₂ c , eq₂ | inj₂ b′ , eq₃ with
inj₁ a ≡⟨ P.sym $ to-from f eq₂ ⟩
from f ⟨$⟩ inj₂ c ≡⟨ eq₃ ⟩
inj₂ b′ ∎
... | ()
g∘g′ | inj₁ a , eq₁ | inj₂ c , eq₂ | inj₁ a′ , eq₃ with inspect (from f ⟨$⟩ inj₁ a′)
g∘g′ | inj₁ a , eq₁ | inj₂ c , eq₂ | inj₁ a′ , eq₃ | inj₁ a″ , eq₄ = ⊥-elim $ from-hyp eq₃ eq₄
g∘g′ | inj₁ a , eq₁ | inj₂ c , eq₂ | inj₁ a′ , eq₃ | inj₂ b′ , eq₄ = inj₂-injective (
let lemma =
inj₁ a′ ≡⟨ P.sym eq₃ ⟩
from f ⟨$⟩ inj₂ c ≡⟨ to-from f eq₂ ⟩
inj₁ a ∎
in
inj₂ b′ ≡⟨ P.sym eq₄ ⟩
from f ⟨$⟩ inj₁ a′ ≡⟨ P.cong ((from f ⟨$⟩_) ∘ inj₁) $ inj₁-injective lemma ⟩
from f ⟨$⟩ inj₁ a ≡⟨ to-from f eq₁ ⟩
inj₂ b ∎)
∼→⊎↔⊎ :
∀ {x : A} {xs ys} →
x ∷ xs ∼[ bag ] x ∷ ys →
∀ {z} → (z ≡ x ⊎ z ∈ xs) ↔ (z ≡ x ⊎ z ∈ ys)
∼→⊎↔⊎ {x} {xs} {ys} x∷xs≈x∷ys {z} =
(z ≡ x ⊎ z ∈ xs) ↔⟨ ∷↔ _ ⟩
z ∈ x ∷ xs ↔⟨ x∷xs≈x∷ys ⟩
z ∈ x ∷ ys ↔⟨ SK-sym (∷↔ _) ⟩
(z ≡ x ⊎ z ∈ ys) ∎
where
open Related.EquationalReasoning
lemma : ∀ {xs ys} (inv : x ∷ xs ∼[ bag ] x ∷ ys) {z} →
Well-behaved (Inverse.to (∼→⊎↔⊎ inv {z}) ⟨$⟩_)
lemma {xs} inv {b = z∈xs} {a = p} {a′ = q} hyp₁ hyp₂ with
zero ≡⟨⟩
index-of {xs = x ∷ xs} (here p) ≡⟨⟩
index-of {xs = x ∷ xs} (to (∷↔ _) ⟨$⟩ inj₁ p) ≡⟨ P.cong (index-of ∘ (to (∷↔ (_ ≡_)) ⟨$⟩_)) $ P.sym $
to-from (∼→⊎↔⊎ inv) {x = inj₁ p} hyp₂ ⟩
index-of {xs = x ∷ xs} (to (∷↔ _) ⟨$⟩ (from (∼→⊎↔⊎ inv) ⟨$⟩ inj₁ q)) ≡⟨ P.cong index-of $
right-inverse-of (∷↔ _) (from inv ⟨$⟩ here q) ⟩
index-of {xs = x ∷ xs} (to (SK-sym inv) ⟨$⟩ here q) ≡⟨ index-equality-preserved (SK-sym inv) refl ⟩
index-of {xs = x ∷ xs} (to (SK-sym inv) ⟨$⟩ here p) ≡⟨ P.cong index-of $ P.sym $
right-inverse-of (∷↔ _) (from inv ⟨$⟩ here p) ⟩
index-of {xs = x ∷ xs} (to (∷↔ _) ⟨$⟩ (from (∼→⊎↔⊎ inv) ⟨$⟩ inj₁ p)) ≡⟨ P.cong (index-of ∘ (to (∷↔ (_ ≡_)) ⟨$⟩_)) $
to-from (∼→⊎↔⊎ inv) {x = inj₂ z∈xs} hyp₁ ⟩
index-of {xs = x ∷ xs} (to (∷↔ _) ⟨$⟩ inj₂ z∈xs) ≡⟨⟩
index-of {xs = x ∷ xs} (there z∈xs) ≡⟨⟩
suc (index-of {xs = xs} z∈xs) ∎
where
open Inverse
open P.≡-Reasoning
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