------------------------------------------------------------------------
-- The Agda standard library
--
-- Many properties which hold for `∼` also hold for `flip ∼`. Unlike
-- the module `Relation.Binary.Construct.Flip` this module does not
-- flip the underlying equality.
------------------------------------------------------------------------

{-# OPTIONS --without-K --safe #-}

open import Relation.Binary

module Relation.Binary.Construct.Converse where

open import Data.Product
open import Function.Base using (flip; _∘_)
open import Level using (Level)

private
  variable
    a b p ℓ ℓ₁ ℓ₂ : Level
    A B : Set a
    ≈ ∼ ≤ < : Rel A ℓ

------------------------------------------------------------------------
-- Properties

module _ (∼ : Rel A ℓ) where

  refl : Reflexive ∼ → Reflexive (flip ∼)
  refl refl = refl

  sym : Symmetric ∼ → Symmetric (flip ∼)
  sym sym = sym

  trans : Transitive ∼ → Transitive (flip ∼)
  trans trans = flip trans

  asym : Asymmetric ∼ → Asymmetric (flip ∼)
  asym asym = asym

  total : Total ∼ → Total (flip ∼)
  total total x y = total y x

  resp : ∀ {p} (P : A → Set p) → Symmetric ∼ →
             P Respects ∼ → P Respects (flip ∼)
  resp _ sym resp ∼ = resp (sym ∼)

  max : ∀ {⊥} → Minimum ∼ ⊥ → Maximum (flip ∼) ⊥
  max min = min

  min : ∀ {⊤} → Maximum ∼ ⊤ → Minimum (flip ∼) ⊤
  min max = max

module _ {≈ : Rel A ℓ₁} (∼ : Rel A ℓ₂) where

  reflexive : Symmetric ≈ → (≈ ⇒ ∼) → (≈ ⇒ flip ∼)
  reflexive sym impl = impl ∘ sym

  irrefl : Symmetric ≈ → Irreflexive ≈ ∼ → Irreflexive ≈ (flip ∼)
  irrefl sym irrefl x≈y y∼x = irrefl (sym x≈y) y∼x

  antisym : Antisymmetric ≈ ∼ → Antisymmetric ≈ (flip ∼)
  antisym antisym = flip antisym

  compare : Trichotomous ≈ ∼ → Trichotomous ≈ (flip ∼)
  compare cmp x y with cmp x y
  ... | tri< x<y x≉y y≮x = tri> y≮x x≉y x<y
  ... | tri≈ x≮y x≈y y≮x = tri≈ y≮x x≈y x≮y
  ... | tri> x≮y x≉y y<x = tri< y<x x≉y x≮y

module _ (∼₁ : Rel A ℓ₁) (∼₂ : Rel A ℓ₂) where

  resp₂ : ∼₁ Respects₂ ∼₂ → (flip ∼₁) Respects₂ ∼₂
  resp₂ (resp₁ , resp₂) = resp₂ , resp₁

module _ (∼ : REL A B ℓ) where

  dec : Decidable ∼ → Decidable (flip ∼)
  dec dec = flip dec

------------------------------------------------------------------------
-- Structures

isEquivalence : IsEquivalence ≈ → IsEquivalence (flip ≈)
isEquivalence {≈ = ≈} eq = record
  { refl  = refl  ≈ Eq.refl
  ; sym   = sym   ≈ Eq.sym
  ; trans = trans ≈ Eq.trans
  } where module Eq = IsEquivalence eq

isDecEquivalence : IsDecEquivalence ≈ → IsDecEquivalence (flip ≈)
isDecEquivalence {≈ = ≈} eq = record
  { isEquivalence = isEquivalence Dec.isEquivalence
  ; _≟_           = dec ≈ Dec._≟_
  } where module Dec = IsDecEquivalence eq

isPreorder : IsPreorder ≈ ∼ → IsPreorder ≈ (flip ∼)
isPreorder {≈ = ≈} {∼ = ∼} O = record
  { isEquivalence = O.isEquivalence
  ; reflexive     = reflexive ∼ O.Eq.sym O.reflexive
  ; trans         = trans ∼ O.trans
  } where module O = IsPreorder O

isTotalPreorder : IsTotalPreorder ≈ ∼ → IsTotalPreorder ≈ (flip ∼)
isTotalPreorder O = record
  { isPreorder = isPreorder O.isPreorder
  ; total      = total _ O.total
  } where module O = IsTotalPreorder O

isPartialOrder : IsPartialOrder ≈ ≤ → IsPartialOrder ≈ (flip ≤)
isPartialOrder {≤ = ≤} O = record
  { isPreorder = isPreorder O.isPreorder
  ; antisym    = antisym ≤ O.antisym
  } where module O = IsPartialOrder O

isTotalOrder : IsTotalOrder ≈ ≤ → IsTotalOrder ≈ (flip ≤)
isTotalOrder O = record
  { isPartialOrder = isPartialOrder O.isPartialOrder
  ; total          = total _ O.total
  } where module O = IsTotalOrder O

isDecTotalOrder : IsDecTotalOrder ≈ ≤ → IsDecTotalOrder ≈ (flip ≤)
isDecTotalOrder O = record
  { isTotalOrder = isTotalOrder O.isTotalOrder
  ; _≟_          = O._≟_
  ; _≤?_         = dec _ O._≤?_
  } where module O = IsDecTotalOrder O

isStrictPartialOrder : IsStrictPartialOrder ≈ < →
                       IsStrictPartialOrder ≈ (flip <)
isStrictPartialOrder {< = <} O = record
  { isEquivalence = O.isEquivalence
  ; irrefl        = irrefl < O.Eq.sym O.irrefl
  ; trans         = trans < O.trans
  ; <-resp-≈      = resp₂ _ _ O.<-resp-≈
  } where module O = IsStrictPartialOrder O

isStrictTotalOrder : IsStrictTotalOrder ≈ < →
                     IsStrictTotalOrder ≈ (flip <)
isStrictTotalOrder {< = <} O = record
  { isEquivalence = O.isEquivalence
  ; trans         = trans < O.trans
  ; compare       = compare _ O.compare
  } where module O = IsStrictTotalOrder O

------------------------------------------------------------------------
-- Bundles

setoid : Setoid a ℓ → Setoid a ℓ
setoid S = record
  { isEquivalence = isEquivalence S.isEquivalence
  } where module S = Setoid S

decSetoid : DecSetoid a ℓ → DecSetoid a ℓ
decSetoid S = record
  { isDecEquivalence = isDecEquivalence S.isDecEquivalence
  } where module S = DecSetoid S

preorder : Preorder a ℓ₁ ℓ₂ → Preorder a ℓ₁ ℓ₂
preorder O = record
  { isPreorder = isPreorder O.isPreorder
  } where module O = Preorder O

totalPreorder : TotalPreorder a ℓ₁ ℓ₂ → TotalPreorder a ℓ₁ ℓ₂
totalPreorder O = record
  { isTotalPreorder = isTotalPreorder O.isTotalPreorder
  } where module O = TotalPreorder O

poset : Poset a ℓ₁ ℓ₂ → Poset a ℓ₁ ℓ₂
poset O = record
  { isPartialOrder = isPartialOrder O.isPartialOrder
  } where module O = Poset O

totalOrder : TotalOrder a ℓ₁ ℓ₂ → TotalOrder a ℓ₁ ℓ₂
totalOrder O = record
  { isTotalOrder = isTotalOrder O.isTotalOrder
  } where module O = TotalOrder O

decTotalOrder : DecTotalOrder a ℓ₁ ℓ₂ → DecTotalOrder a ℓ₁ ℓ₂
decTotalOrder O = record
  { isDecTotalOrder = isDecTotalOrder O.isDecTotalOrder
  } where module O = DecTotalOrder O

strictPartialOrder : StrictPartialOrder a ℓ₁ ℓ₂ →
                     StrictPartialOrder a ℓ₁ ℓ₂
strictPartialOrder O = record
  { isStrictPartialOrder = isStrictPartialOrder O.isStrictPartialOrder
  } where module O = StrictPartialOrder O

strictTotalOrder : StrictTotalOrder a ℓ₁ ℓ₂ →
                   StrictTotalOrder a ℓ₁ ℓ₂
strictTotalOrder O = record
  { isStrictTotalOrder = isStrictTotalOrder O.isStrictTotalOrder
  } where module O = StrictTotalOrder O