------------------------------------------------------------------------
-- The Agda standard library
--
-- Indexed binary relations
------------------------------------------------------------------------

-- The contents of this module should be accessed via
-- `Relation.Binary.Indexed.Heterogeneous`.

{-# OPTIONS --cubical-compatible --safe #-}

module Relation.Binary.Indexed.Heterogeneous.Core where

open import Level using (Level)
import Relation.Binary.Core as B using (Rel; REL; _⇒_)

------------------------------------------------------------------------
-- Indexed binary relations

-- Heterogeneous types

IREL : ∀ {i₁ i₂ a₁ a₂} {I₁ : Set i₁} {I₂ : Set i₂} →
      (I₁ → Set a₁) → (I₂ → Set a₂) → (ℓ : Level) → Set _
IREL A₁ A₂ ℓ = ∀ {i₁ i₂} → A₁ i₁ → A₂ i₂ → Set ℓ

-- Homogeneous types

IRel : ∀ {i a} {I : Set i} → (I → Set a) → (ℓ : Level) → Set _
IRel A ℓ = IREL A A ℓ

------------------------------------------------------------------------
-- Generalised implication.

infixr  _=[_]⇒_

_=[_]⇒_ : ∀ {a b ℓ₁ ℓ₂} {A : Set a} {B : A → Set b} →
          B.Rel A ℓ₁ → ((x : A) → B x) → IRel B ℓ₂ → Set _
P =[ f ]⇒ Q = ∀ {i j} → P i j → Q (f i) (f j)