diff -ru patience-0.1.1/Data/Algorithm/Patience.hs patience-modified/Data/Algorithm/Patience.hs
--- patience-0.1.1/Data/Algorithm/Patience.hs	2011-08-17 08:08:14.000000000 +0800
+++ patience-modified/Data/Algorithm/Patience.hs	2018-07-11 15:17:45.021338649 +0800
@@ -15,6 +15,7 @@
 import Data.Sequence ( (<|), (|>), (><), ViewL(..), ViewR(..) )
 import qualified Data.Foldable as F
 import qualified Data.Map      as M
+import qualified Data.Map.Strict as MS
 import qualified Data.IntMap   as IM
 
 import Data.List
@@ -68,7 +69,7 @@
 -- Elements whose second component appears exactly once.
 unique :: (Ord t) => S.Seq (a,t) -> M.Map t a
 unique = M.mapMaybe id . F.foldr ins M.empty where
-  ins (a,x) = M.insertWith' (\_ _ -> Nothing) x (Just a)
+  ins (a,x) = MS.insertWith (\_ _ -> Nothing) x (Just a)
 
 -- Given two sequences of numbered "lines", returns a list of points
 -- where unique lines match up.