Refactor Data.List.Relation.Binary.Permutation.*, part I (#2333)

* move `steps` towards deprecation in `Homogeneous`

* deprecate `steps`; refactor `Setoid` proofs and equaiotnal reasoning combinators

* extensive refactoring

* tidy up

* add equivalence with `Setoid` representation

* removed buggy `PermutationReasoning` syntax

* refactored; removed buggy `PermutationReasoning` syntax

* `CHANGELOG`

* final fix-ups

* tighten `import`s

* tighten `import`s

* redundant constructor aliases

* fix-up `Reasoning` steps with the alias

* use aliases

* more `import` tightening

* refactor: encapsulate and tighten up

* avoid `PermutationReasoning` custom combinators

* fix up `CHANGELOG`

* encapsulate helper function

* revert changes

* review comments

* `fix-whitespace`

* toned down the comment on `steps`

* remove use of infix `insert`

* revert other deprecation

* no need for qualification

* remove deprecation banner

* three paras of commentary on the new transitivity proofs

* missing entry

* missing terminator

* response to review comments

* `with` to `let`

* fixed `BagAndSetEquality`

* fixed qualified `import` bug introduced during merge conflict resolution

* Update CHANGELOG.md

Deleted spurious attribution of the lemmas in `Data.List.Properties` about `product` to `Data.List.Relation.Unary.All.Properties`. Hope this fixes things now!

---------

Co-authored-by: MatthewDaggitt <[email protected]>

Author: jamesmckinna

CHANGELOG.md

@@ -59,6 +59,13 @@ Deprecated names
   normalise-correct  ↦  Algebra.Solver.Monoid.Normal.correct
   ```
 
+* In `Data.List.Relation.Binary.Permutation.Setoid.Properties`:
+  ```agda
+  split  ↦  ↭-split
+  ```
+  with a more informative type (see below).
+  ```
+
 * In `Data.Vec.Properties`:
   ```agda
   ++-assoc _      ↦  ++-assoc-eqFree
@@ -167,11 +174,6 @@ Additions to existing modules
   concatMap-++ : concatMap f (xs ++ ys) ≡ concatMap f xs ++ concatMap f ys
   ```
 
-* In `Data.List.Relation.Unary.All`:
-  ```agda
-  search : Decidable P → ∀ xs → All (∁ P) xs ⊎ Any P xs
-  ```
-
 * In `Data.List.Relation.Unary.Any.Properties`:
   ```agda
   concatMap⁺ : Any (Any P ∘ f) xs → Any P (concatMap f xs)
@@ -194,12 +196,60 @@ Additions to existing modules
   ++⁺ˡ : ∀ zs → ws ≋ xs → ws ++ zs ≋ xs ++ zs
   ```
 
+* In `Data.List.Relation.Binary.Permutation.Homogeneous`:
+  ```agda
+  steps : Permutation R xs ys → ℕ
+  ```
+
+* In `Data.List.Relation.Binary.Permutation.Propositional`:
+  constructor aliases
+  ```agda
+  ↭-refl  : Reflexive _↭_
+  ↭-prep  : ∀ x → xs ↭ ys → x ∷ xs ↭ x ∷ ys
+  ↭-swap  : ∀ x y → xs ↭ ys → x ∷ y ∷ xs ↭ y ∷ x ∷ ys
+  ```
+  and properties
+  ```agda
+  ↭-reflexive-≋ : _≋_ ⇒ _↭_
+  ↭⇒↭ₛ          : _↭_  ⇒ _↭ₛ_
+  ↭ₛ⇒↭          : _↭ₛ_ ⇒ _↭_
+  ```
+  where `_↭ₛ_` is the `Setoid (setoid _)` instance of `Permutation`
+
+* In `Data.List.Relation.Binary.Permutation.Propositional.Properties`:
+  ```agda
+  Any-resp-[σ∘σ⁻¹] : (σ : xs ↭ ys) (iy : Any P ys) →
+                     Any-resp-↭ (trans (↭-sym σ) σ) iy ≡ iy
+  ∈-resp-[σ∘σ⁻¹]   : (σ : xs ↭ ys) (iy : y ∈ ys) →
+                     ∈-resp-↭ (trans (↭-sym σ) σ) iy ≡ iy
+  product-↭        : product Preserves _↭_ ⟶ _≡_
+  ```
+
+* In `Data.List.Relation.Binary.Permutation.Setoid`:
+  ```agda
+  ↭-reflexive-≋ : _≋_  ⇒ _↭_
+  ↭-transˡ-≋    : LeftTrans _≋_ _↭_
+  ↭-transʳ-≋    : RightTrans _↭_ _≋_
+  ↭-trans′      : Transitive _↭_
+  ```
+
+* In `Data.List.Relation.Binary.Permutation.Setoid.Properties`:
+  ```agda
+  ↭-split : xs ↭ (as ++ [ v ] ++ bs) →
+            ∃₂ λ ps qs → xs ≋ (ps ++ [ v ] ++ qs) × (ps ++ qs) ↭ (as ++ bs)
+  drop-∷  : x ∷ xs ↭ x ∷ ys → xs ↭ ys
+  ```
+
 * In `Data.List.Relation.Binary.Pointwise`:
   ```agda
   ++⁺ʳ : Reflexive R → ∀ xs → (xs ++_) Preserves (Pointwise R) ⟶ (Pointwise R)
   ++⁺ˡ : Reflexive R → ∀ zs → (_++ zs) Preserves (Pointwise R) ⟶ (Pointwise R)
   ```
 
+* In `Data.List.Relation.Unary.All`:
+  ```agda
+  search : Decidable P → ∀ xs → All (∁ P) xs ⊎ Any P xs
+
 * In `Data.List.Relation.Binary.Subset.Setoid.Properties`:
   ```agda
   ∷⊈[]   : x ∷ xs ⊈ []

src/Data/List/Relation/Binary/BagAndSetEquality.agda

@@ -27,9 +27,9 @@ open import Data.List.Membership.Propositional.Properties
 open import Data.List.Relation.Binary.Subset.Propositional.Properties
   using (⊆-preorder)
 open import Data.List.Relation.Binary.Permutation.Propositional
-  using (_↭_; ↭-sym; refl; module PermutationReasoning)
+  using (_↭_; ↭-refl; ↭-sym; ↭-prep; module PermutationReasoning)
 open import Data.List.Relation.Binary.Permutation.Propositional.Properties
-  using (∈-resp-↭; ∈-resp-[σ⁻¹∘σ]; ↭-sym-involutive; shift; ++-comm)
+  using (∈-resp-↭; ∈-resp-[σ⁻¹∘σ]; ∈-resp-[σ∘σ⁻¹]; shift; ++-comm)
 open import Data.Product.Base as Product using (∃; _,_; proj₁; proj₂; _×_)
 import Data.Product.Function.Dependent.Propositional as Σ
 open import Data.Sum.Base as Sum using (_⊎_; [_,_]′; inj₁; inj₂)
@@ -574,29 +574,18 @@ drop-cons {x = x} {xs} {ys} x∷xs≈x∷ys =
 
 
 ------------------------------------------------------------------------
--- Relationships to other relations
+-- Relationships to propositional permutation
 
 ↭⇒∼bag : _↭_ {A = A} ⇒ _∼[ bag ]_
-↭⇒∼bag xs↭ys {v} = mk↔ₛ′ (to xs↭ys) (from xs↭ys) (to∘from xs↭ys) (from∘to xs↭ys)
-  where
-  to : ∀ {xs ys} → xs ↭ ys → v ∈ xs → v ∈ ys
-  to xs↭ys = ∈-resp-↭ xs↭ys
-
-  from : ∀ {xs ys} → xs ↭ ys → v ∈ ys → v ∈ xs
-  from xs↭ys = ∈-resp-↭ (↭-sym xs↭ys)
-
-  from∘to : ∀ {xs ys} (p : xs ↭ ys) (q : v ∈ xs) → from p (to p q) ≡ q
-  from∘to = ∈-resp-[σ⁻¹∘σ]
-
-  to∘from : ∀ {xs ys} (p : xs ↭ ys) (q : v ∈ ys) → to p (from p q) ≡ q
-  to∘from p with res ← from∘to (↭-sym p) rewrite ↭-sym-involutive p = res
+↭⇒∼bag xs↭ys {v} =
+  mk↔ₛ′ (∈-resp-↭ xs↭ys) (∈-resp-↭ (↭-sym xs↭ys)) (∈-resp-[σ∘σ⁻¹] xs↭ys) (∈-resp-[σ⁻¹∘σ] xs↭ys)
 
 ∼bag⇒↭ : _∼[ bag ]_ ⇒ _↭_ {A = A}
-∼bag⇒↭ {A = A} {[]} eq with refl ← empty-unique (↔-sym eq) = refl
+∼bag⇒↭ {A = A} {[]}     eq with refl ← empty-unique (↔-sym eq) = ↭-refl
 ∼bag⇒↭ {A = A} {x ∷ xs} eq
-  with zs₁ , zs₂ , p ← ∈-∃++ (Inverse.to (eq {x}) (here ≡.refl)) rewrite p = begin
-    x ∷ xs           <⟨ ∼bag⇒↭ (drop-cons (↔-trans eq (comm zs₁ (x ∷ zs₂)))) ⟩
-    x ∷ (zs₂ ++ zs₁) <⟨ ++-comm zs₂ zs₁ ⟩
+  with zs₁ , zs₂ , refl ← ∈-∃++ (Inverse.to (eq {x}) (here refl)) = begin
+    x ∷ xs           ↭⟨ ↭-prep x (∼bag⇒↭ (drop-cons (↔-trans eq (comm zs₁ (x ∷ zs₂))))) ⟩
+    x ∷ (zs₂ ++ zs₁) ↭⟨ ↭-prep x (++-comm zs₂ zs₁) ⟩
     x ∷ (zs₁ ++ zs₂) ↭⟨ shift x zs₁ zs₂ ⟨
     zs₁ ++ x ∷ zs₂   ∎
     where

src/Data/List/Relation/Binary/Permutation/Homogeneous.agda

@@ -11,8 +11,8 @@ module Data.List.Relation.Binary.Permutation.Homogeneous where
 open import Data.List.Base using (List; _∷_)
 open import Data.List.Relation.Binary.Pointwise.Base as Pointwise
   using (Pointwise)
-open import Data.List.Relation.Binary.Pointwise.Properties as Pointwise
-  using (symmetric)
+import Data.List.Relation.Binary.Pointwise.Properties as Pointwise
+open import Data.Nat.Base using (ℕ; suc; _+_)
 open import Level using (Level; _⊔_)
 open import Relation.Binary.Core using (Rel; _⇒_)
 open import Relation.Binary.Bundles using (Setoid)
@@ -59,3 +59,11 @@ map R⇒S (refl xs∼ys)         = refl (Pointwise.map R⇒S xs∼ys)
 map R⇒S (prep e xs∼ys)       = prep (R⇒S e) (map R⇒S xs∼ys)
 map R⇒S (swap e₁ e₂ xs∼ys)   = swap (R⇒S e₁) (R⇒S e₂) (map R⇒S xs∼ys)
 map R⇒S (trans xs∼ys ys∼zs)  = trans (map R⇒S xs∼ys) (map R⇒S ys∼zs)
+
+-- Measures the number of constructors, can be useful for termination proofs
+
+steps : ∀ {R : Rel A r} {xs ys} → Permutation R xs ys → ℕ
+steps (refl _)            = 1
+steps (prep _ xs↭ys)      = suc (steps xs↭ys)
+steps (swap _ _ xs↭ys)    = suc (steps xs↭ys)
+steps (trans xs↭ys ys↭zs) = steps xs↭ys + steps ys↭zs

src/Data/List/Relation/Binary/Permutation/Propositional.agda

@@ -10,14 +10,22 @@ module Data.List.Relation.Binary.Permutation.Propositional
   {a} {A : Set a} where
 
 open import Data.List.Base using (List; []; _∷_)
+open import Data.List.Relation.Binary.Equality.Propositional using (_≋_; ≋⇒≡)
 open import Relation.Binary.Core using (Rel; _⇒_)
 open import Relation.Binary.Bundles using (Setoid)
 open import Relation.Binary.Structures using (IsEquivalence)
 open import Relation.Binary.Definitions using (Reflexive; Transitive)
-open import Relation.Binary.PropositionalEquality.Core using (_≡_; refl)
+open import Relation.Binary.PropositionalEquality as ≡ using (_≡_; refl)
 import Relation.Binary.Reasoning.Setoid as EqReasoning
 open import Relation.Binary.Reasoning.Syntax
 
+import Data.List.Relation.Binary.Permutation.Setoid as Permutation
+
+private
+  variable
+    x y z v w : A
+    ws xs ys zs : List A
+
 ------------------------------------------------------------------------
 -- An inductive definition of permutation
 
@@ -30,21 +38,32 @@ open import Relation.Binary.Reasoning.Syntax
 infix 3 _↭_
 
 data _↭_ : Rel (List A) a where
-  refl  : ∀ {xs}        → xs ↭ xs
-  prep  : ∀ {xs ys} x   → xs ↭ ys → x ∷ xs ↭ x ∷ ys
-  swap  : ∀ {xs ys} x y → xs ↭ ys → x ∷ y ∷ xs ↭ y ∷ x ∷ ys
-  trans : ∀ {xs ys zs}  → xs ↭ ys → ys ↭ zs → xs ↭ zs
+  refl  : xs ↭ xs
+  prep  : ∀ x → xs ↭ ys → x ∷ xs ↭ x ∷ ys
+  swap  : ∀ x y → xs ↭ ys → x ∷ y ∷ xs ↭ y ∷ x ∷ ys
+  trans : xs ↭ ys → ys ↭ zs → xs ↭ zs
+
+-- Constructor aliases
+
+↭-refl : Reflexive _↭_
+↭-refl = refl
+
+↭-prep  : ∀ x → xs ↭ ys → x ∷ xs ↭ x ∷ ys
+↭-prep = prep
+
+↭-swap  : ∀ x y → xs ↭ ys → x ∷ y ∷ xs ↭ y ∷ x ∷ ys
+↭-swap = swap
 
 ------------------------------------------------------------------------
 -- _↭_ is an equivalence
 
 ↭-reflexive : _≡_ ⇒ _↭_
-↭-reflexive refl = refl
+↭-reflexive refl = ↭-refl
 
-↭-refl : Reflexive _↭_
-↭-refl = refl
+↭-reflexive-≋ : _≋_ ⇒ _↭_
+↭-reflexive-≋ xs≋ys = ↭-reflexive (≋⇒≡ xs≋ys)
 
-↭-sym : ∀ {xs ys} → xs ↭ ys → ys ↭ xs
+↭-sym : xs ↭ ys → ys ↭ xs
 ↭-sym refl                = refl
 ↭-sym (prep x xs↭ys)      = prep x (↭-sym xs↭ys)
 ↭-sym (swap x y xs↭ys)    = swap y x (↭-sym xs↭ys)
@@ -58,7 +77,7 @@ data _↭_ : Rel (List A) a where
 
 ↭-isEquivalence : IsEquivalence _↭_
 ↭-isEquivalence = record
-  { refl  = refl
+  { refl  = ↭-refl
   ; sym   = ↭-sym
   ; trans = ↭-trans
   }
@@ -68,6 +87,28 @@ data _↭_ : Rel (List A) a where
   { isEquivalence = ↭-isEquivalence
   }
 
+------------------------------------------------------------------------
+-- _↭_ is equivalent to `Setoid`-based permutation
+
+private
+  open module ↭ₛ = Permutation (≡.setoid A)
+    using ()
+    renaming (_↭_ to _↭ₛ_)
+
+↭⇒↭ₛ : xs ↭ ys → xs ↭ₛ ys
+↭⇒↭ₛ refl         = ↭ₛ.↭-refl
+↭⇒↭ₛ (prep x p)   = ↭ₛ.↭-prep x (↭⇒↭ₛ p)
+↭⇒↭ₛ (swap x y p) = ↭ₛ.↭-swap x y (↭⇒↭ₛ p)
+↭⇒↭ₛ (trans p q)  = ↭ₛ.↭-trans′ (↭⇒↭ₛ p) (↭⇒↭ₛ q)
+
+
+↭ₛ⇒↭ : _↭ₛ_ ⇒ _↭_
+↭ₛ⇒↭ (↭ₛ.refl xs≋ys)       = ↭-reflexive-≋ xs≋ys
+↭ₛ⇒↭ (↭ₛ.prep refl p)      = ↭-prep _ (↭ₛ⇒↭ p)
+↭ₛ⇒↭ (↭ₛ.swap refl refl p) = ↭-swap _ _ (↭ₛ⇒↭ p)
+↭ₛ⇒↭ (↭ₛ.trans p q)        = ↭-trans (↭ₛ⇒↭ p) (↭ₛ⇒↭ q)
+
+
 ------------------------------------------------------------------------
 -- A reasoning API to chain permutation proofs and allow "zooming in"
 -- to localised reasoning.
@@ -89,12 +130,12 @@ module PermutationReasoning where
   -- Skip reasoning on the first element
   step-prep : ∀ x xs {ys zs : List A} → (x ∷ ys) IsRelatedTo zs →
               xs ↭ ys → (x ∷ xs) IsRelatedTo zs
-  step-prep x xs rel xs↭ys = relTo (trans (prep x xs↭ys) (begin rel))
+  step-prep x xs rel xs↭ys = ↭-go (↭-prep x xs↭ys) rel
 
   -- Skip reasoning about the first two elements
   step-swap : ∀ x y xs {ys zs : List A} → (y ∷ x ∷ ys) IsRelatedTo zs →
               xs ↭ ys → (x ∷ y ∷ xs) IsRelatedTo zs
-  step-swap x y xs rel xs↭ys = relTo (trans (swap x y xs↭ys) (begin rel))
+  step-swap x y xs rel xs↭ys = ↭-go (↭-swap x y xs↭ys) rel
 
   syntax step-prep x xs y↭z x↭y = x ∷ xs <⟨ x↭y ⟩ y↭z
   syntax step-swap x y xs y↭z x↭y = x ∷ y ∷ xs <<⟨ x↭y ⟩ y↭z