------------------------------------------------------------------------
-- Some properties imply others
------------------------------------------------------------------------

{-# OPTIONS --universe-polymorphism #-}

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

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  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} 
  _<_ Respects₂ _≈_  Symmetric _≈_ 
  Trichotomous _≈_ _<_  Irreflexive _≈_ _<_
tri⟶irr resp sym tri = asym⟶irr resp sym (tri⟶asym tri)

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))