revised longestElement

1 files changed, 1 insertions, 1 deletions

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