From 30fece6537622595dc0853514cc850227cdd169f Mon Sep 17 00:00:00 2001
From: Tissevert <tissevert+devel@marvid.fr>
Date: Mon, 24 Feb 2020 21:39:02 +0100
Subject: [PATCH] Notice the 'edit' I exported earlier could be reused to
 simplify the w implementation of the proof that Box is a transitive relation

---
 .gitignore     | 1 +
 src/PDF/Box.hs | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/.gitignore b/.gitignore
index ebadcab..ad2660f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,3 @@
 dist*/
 .ghc.environment.*
+cabal.project.local
diff --git a/src/PDF/Box.hs b/src/PDF/Box.hs
index a72ff4e..f36b199 100644
--- a/src/PDF/Box.hs
+++ b/src/PDF/Box.hs
@@ -25,7 +25,7 @@ modifyAt i f = get >>= edit i f >>= put
 
 instance (Box m i a b, Box m j b c) => Box m (i, j) a c where
   r (i, j) a = r i a >>= r j
-  w (i, j) a c = r i a >>= flip (w j) c >>= w i a
+  w (i, j) a c = edit i (flip (w j) c) a
 
 infixr 6 .@
 (.@) :: a -> b -> (a, b)