I want a function that changes (1 to 0) on a list, when number of 1's isn't even. I have done these functions: 1) Sees if the lines in a list are even or not: parityLine :: [[Int]] -> [Bool] parityLine [] =[] parityLine (x:xs) |sum(x) `mod` 2 == 0 = True:(parityLine(xs)) |otherwise = False:(parityLine(xs)) 2) Sum the corresponding elements on a list of lists: sumPositions :: [[Int]] -> [Int] sumPositions [] = [] sumPositions (x:xs) = foldl (zipWith (+)) (repeat 0) (x:xs) 3) Sees if the columns in a list are even or not: parityColumn :: [Int] -> [Bool] parityColumn [] = [] parityColumn (x:xs) |head(x:xs) `mod` 2 == 0 = True:parityColumn(xs) |otherwise = False:parityColumn(xs) 4) Does the operation or with two boolean lists: bol :: [Bool] -> [Bool] -> [[Bool]] bol [] _ = [] bol (x:xs) (y:ys)= (map (||x) (y:ys)):(bol xs (y:ys)) 5) Correct List: correct :: [[Int]] -> [[Bool]] correct [] = [] correct (x:xs)=(bol(parityLine (x:xs))(parityColumn(sumPositions(x:xs)))) So what I want is to alter the function correct to [[Int]]-[[Int]] that does this: My Int list(x:xs) With my correct function applied [[0,0,1,1], [[True,True,False,True], [1,0,1,1], [True,True,True,True], [0,1,0,1], [True,True,True,True] [1,1,1,1]] [True,True,True,True]] Now I can see that in the first line third column, False, so I have to correct that number 1 to have a number of 1's even. Result I want that function correct does: [[0,0,0,1], [1,0,1,1], [0,1,0,1], [1,1,1,1]] Thanks.