------------------------------------------------------------------------
-- The Agda standard library
--
-- Some properties imply others
------------------------------------------------------------------------

module Relation.Binary.Consequences where

open import Relation.Binary.Core hiding (refl)
open import Relation.Nullary
open import Relation.Binary.PropositionalEquality.Core
open import Function
open import Data.Sum
open import Data.Product
open import Data.Empty

-- Some of the definitions can be found in the following module:

open import Relation.Binary.Consequences.Core public

Total : ∀ {a ℓ} {A : Set a} → Rel A ℓ → Set _
Total _∼_ = ∀ x y → (x ∼ y) ⊎ (y ∼ x)

trans∧irr⟶asym :
  ∀ {a ℓ₁ ℓ₂} {A : Set a} → {_≈_ : Rel A ℓ₁} {_<_ : Rel A ℓ₂} →
  Reflexive _≈_ →
  Transitive _<_ → Irreflexive _≈_ _<_ → Asymmetric _<_
trans∧irr⟶asym refl trans irrefl = λ x<y y<x →
  irrefl refl (trans x<y y<x)

irr∧antisym⟶asym :
  ∀ {a ℓ₁ ℓ₂} {A : Set a} {_≈_ : Rel A ℓ₁} {_<_ : Rel A ℓ₂} →
  Irreflexive _≈_ _<_ → Antisymmetric _≈_ _<_ → Asymmetric _<_
irr∧antisym⟶asym irrefl antisym = λ x<y y<x →
  irrefl (antisym x<y y<x) x<y

asym⟶antisym :
  ∀ {a ℓ₁ ℓ₂} {A : Set a} {_≈_ : Rel A ℓ₁} {_<_ : Rel A ℓ₂} →
  Asymmetric _<_ → Antisymmetric _≈_ _<_
asym⟶antisym asym x<y y<x = ⊥-elim (asym x<y y<x)

asym⟶irr :
  ∀ {a ℓ₁ ℓ₂} {A : Set a} {_≈_ : Rel A ℓ₁} {_<_ : Rel A ℓ₂} →
  _<_ Respects₂ _≈_ → Symmetric _≈_ →
  Asymmetric _<_ → Irreflexive _≈_ _<_
asym⟶irr {_<_ = _<_} resp sym asym {x} {y} x≈y x<y = asym x<y y<x
  where
  y<y : y < y
  y<y = proj₂ resp x≈y x<y
  y<x : y < x
  y<x = proj₁ resp (sym x≈y) y<y

total⟶refl :
  ∀ {a ℓ₁ ℓ₂} {A : Set a} {_≈_ : Rel A ℓ₁} {_∼_ : Rel A ℓ₂} →
  _∼_ Respects₂ _≈_ → Symmetric _≈_ →
  Total _∼_ → _≈_ ⇒ _∼_
total⟶refl {_≈_ = _≈_} {_∼_ = _∼_} resp sym total = refl
  where
  refl : _≈_ ⇒ _∼_
  refl {x} {y} x≈y with total x y
  ...              | inj₁ x∼y = x∼y
  ...              | inj₂ y∼x =
    proj₁ resp x≈y (proj₂ resp (sym x≈y) y∼x)

total+dec⟶dec :
  ∀ {a ℓ₁ ℓ₂} {A : Set a} {_≈_ : Rel A ℓ₁} {_≤_ : Rel A ℓ₂} →
  _≈_ ⇒ _≤_ → Antisymmetric _≈_ _≤_ →
  Total _≤_ → Decidable _≈_ → Decidable _≤_
total+dec⟶dec {_≈_ = _≈_} {_≤_ = _≤_} refl antisym total _≟_ = dec
  where
  dec : Decidable _≤_
  dec x y with total x y
  ... | inj₁ x≤y = yes x≤y
  ... | inj₂ y≤x with x ≟ y
  ...   | yes  x≈y = yes (refl x≈y)
  ...   | no  ¬x≈y = no (λ x≤y → ¬x≈y (antisym x≤y y≤x))

tri⟶asym :
  ∀ {a ℓ₁ ℓ₂} {A : Set a} {_≈_ : Rel A ℓ₁} {_<_ : Rel A ℓ₂} →
  Trichotomous _≈_ _<_ → Asymmetric _<_
tri⟶asym tri {x} {y} x<y x>y with tri x y
... | tri< _   _ x≯y = x≯y x>y
... | tri≈ _   _ x≯y = x≯y x>y
... | tri> x≮y _ _   = x≮y x<y

tri⟶irr :
  ∀ {a ℓ₁ ℓ₂} {A : Set a} {_≈_ : Rel A ℓ₁} {_<_ : Rel A ℓ₂} →
  Trichotomous _≈_ _<_ → Irreflexive _≈_ _<_
tri⟶irr {_≈_ = _≈_} {_<_} compare = irr
  where
  irr : ∀ {x y} → x ≈ y → ¬ (x < y)
  irr {x} {y} x≈y x<y with compare x y
  ... | tri< _   x≉y y≮x = x≉y x≈y
  ... | tri> x≮y x≉y y<x = x≉y x≈y
  ... | tri≈ x≮y _   y≮x = x≮y x<y

trans∧tri⟶resp≈ :
  ∀ {a ℓ₁ ℓ₂} {A : Set a} {_≈_ : Rel A ℓ₁} {_<_ : Rel A ℓ₂} →
  Symmetric _≈_ → Transitive _≈_ →
  Transitive _<_ → Trichotomous _≈_ _<_ →
  _<_ Respects₂ _≈_
trans∧tri⟶resp≈ {_≈_ = _≈_} {_<_} sym trans <-trans tri =
  respʳ , respˡ
  where
  respʳ : ∀ {x y z} → y ≈ z → x < y → x < z
  respʳ {x} {z = z} y≈z x<y with tri x z
  ... | tri< x<z _ _ = x<z
  ... | tri≈ _ x≈z _ = ⊥-elim (tri⟶irr tri (trans x≈z (sym y≈z)) x<y)
  ... | tri> _ _ z<x = ⊥-elim (tri⟶irr tri (sym y≈z) (<-trans z<x x<y))

  respˡ : ∀ {z x y} → x ≈ y → x < z → y < z
  respˡ {z} {y = y} x≈y x<z with tri y z
  ... | tri< y<z _ _ = y<z
  ... | tri≈ _ y≈z _ = ⊥-elim (tri⟶irr tri (trans x≈y y≈z) x<z)
  ... | tri> _ _ z<y = ⊥-elim (tri⟶irr tri x≈y (<-trans x<z z<y))

tri⟶dec≈ :
  ∀ {a ℓ₁ ℓ₂} {A : Set a} {_≈_ : Rel A ℓ₁} {_<_ : Rel A ℓ₂} →
  Trichotomous _≈_ _<_ → Decidable _≈_
tri⟶dec≈ compare x y with compare x y
... | tri< _ x≉y _ = no  x≉y
... | tri≈ _ x≈y _ = yes x≈y
... | tri> _ x≉y _ = no  x≉y

tri⟶dec< :
  ∀ {a ℓ₁ ℓ₂} {A : Set a} {_≈_ : Rel A ℓ₁} {_<_ : Rel A ℓ₂} →
  Trichotomous _≈_ _<_ → Decidable _<_
tri⟶dec< compare x y with compare x y
... | tri< x<y _ _ = yes x<y
... | tri≈ x≮y _ _ = no  x≮y
... | tri> x≮y _ _ = no  x≮y

map-NonEmpty : ∀ {a b p q} {A : Set a} {B : Set b}
                 {P : REL A B p} {Q : REL A B q} →
               P ⇒ Q → NonEmpty P → NonEmpty Q
map-NonEmpty f x = nonEmpty (f (NonEmpty.proof x))