diff --git a/src/projectEuler/question4.hs b/src/projectEuler/question4.hs
index d5ba537..c27fe1c 100644
--- a/src/projectEuler/question4.hs
+++ b/src/projectEuler/question4.hs
@@ -1,10 +1,19 @@
--- https://projecteuler.net/problem=4
+{-
+https://projecteuler.net/problem=4
+A palindromic number reads the same both ways.
+The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 x 99.
+
+Find the largest palindrome made from the product of two 3-digit numbers.
+-}
 
 import           Debug.Trace (trace)
 
 twoDigitProducts :: [Integer]
 twoDigitProducts =  [ n*m | n <- [10..99], m <- [n..99] ]
 
+threeDigitProducts :: [Integer]
+threeDigitProducts =  [ n*m | n <- [100..999], m <- [n..999] ]
+
 isPalindrome :: Integer -> Bool
 isPalindrome n = all (== True) $ zipWith (==) half half'
   where
@@ -15,7 +24,7 @@ isPalindrome n = all (== True) $ zipWith (==) half half'
     -- n' = trace (show n) $ show n
 
 solve :: Integer
-solve = maximum $ filter isPalindrome twoDigitProducts
+solve = maximum $ filter isPalindrome threeDigitProducts
 
 main :: IO ()
 main = print solve