Martin Escardo and Paulo Oliva 2011

\begin{code}

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

module InfinitePigeon.Equality where

open import InfinitePigeon.Logic

data _≡_ {X : Set} : X → X → Ω where
 reflexivity : {x : X} → x ≡ x

infix   _≡_

two-things-equal-to-a-third-are-equal
 : {X : Set}
   {x y z : X}
 → x ≡ y → x ≡ z → y ≡ z
two-things-equal-to-a-third-are-equal reflexivity reflexivity = reflexivity

transitivity : {X : Set} → {x y z : X} →  x ≡ y  →  y ≡ z  →  x ≡ z
transitivity reflexivity reflexivity = reflexivity

symmetry : {X : Set} → {x y : X} → x ≡ y → y ≡ x
symmetry reflexivity = reflexivity

compositionality : {X Y : Set}
                   (f : X → Y)
                   {x₀ x₁ : X}
                 → x₀ ≡ x₁ →  f x₀ ≡ f x₁
compositionality f reflexivity = reflexivity

predicate-compositionality : {X : Set}
                             (A : X → Ω)
                             {x y : X}
                           → x ≡ y → A x → A y
predicate-compositionality A reflexivity a = a

binary-predicate-compositionality
 : {X Y : Set}
   {A : X → Y → Ω}
   {x x' : X} {y y' : Y}
 → x ≡ x' → y ≡ y' → A x y → A x' y'

binary-predicate-compositionality reflexivity reflexivity a = a

set-compositionality : {I : Set} (X : I → Set) → {i j : I} → i ≡ j → X i → X j
set-compositionality X reflexivity x = x

\end{code}