diff --git a/2021/day13.hs b/2021/day13.hs
index 125e579..40ab4f7 100644
--- a/2021/day13.hs
+++ b/2021/day13.hs
@@ -29,11 +29,10 @@ main = do
     print $ S.size dots1
 
     putStrLn "part 2: "
-    let dots2 = map (\d -> foldl (flip fold) d folds) dots
-    let dots2' = S.fromList dots2
-    let max_x = maximum $ map fst dots2
-    let max_y = maximum $ map snd dots2
+    let dots2 = S.fromList $ map (\d -> foldl (flip fold) d folds) dots
+    let max_x = maximum $ S.map fst dots2
+    let max_y = maximum $ S.map snd dots2
     mapM_ (\y -> do
-            mapM_ (\x -> putChar (if (x,y) `S.member` dots2' then '#' else '.')) [0..max_x]
+            mapM_ (\x -> putChar (if (x,y) `S.member` dots2 then '#' else '.')) [0..max_x]
             putStrLn ""
         ) [0..max_y]