diff --git a/app/Day6.hs b/app/Day6.hs
index f186eda..2dad8be 100644
--- a/app/Day6.hs
+++ b/app/Day6.hs
@@ -7,6 +7,9 @@ import qualified Data.IntMap as M
 import Data.List (foldl')
 import System.Environment (getArgs)
 
+-- TODO: solve part 2 by transposing the matrix before parsing the
+-- numbers.
+
 main :: IO ()
 main = do
   input <- readFile . head =<< getArgs