From 523ba0227915169ad2423caf21d80c0252f26165 Mon Sep 17 00:00:00 2001
From: Jeshiba <baconp@gmail.com>
Date: Wed, 12 Jul 2017 16:03:31 -0400
Subject: revised longestElement

---
 Math/Combinatorics/RootSystem.hs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Math/Combinatorics/RootSystem.hs b/Math/Combinatorics/RootSystem.hs
index 53cf65c..e388a23 100644
--- a/Math/Combinatorics/RootSystem.hs
+++ b/Math/Combinatorics/RootSystem.hs
@@ -76,7 +76,7 @@ longestElement ss = longestElement' [] posRoots
         posRoots = positiveRoots ss
         longestElement' :: [[Q]] -> [[Q]] -> [[Q]]
         longestElement' xs rs = 
-            let ys = (S.fromList ss) S.\\ (S.fromList $ negateM rs) in
+            let ys = (S.fromList ss) S.\\ (S.fromList $ negateM rs) S.\\ (if null xs then S.empty else S.singleton (head xs)) in
                 if S.null ys
                 then xs
                 else let alpha = (head (S.toList ys)) in
-- 
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