markSF :: Int -> Int -> Int -> Square -> Square
markSF start finish i x | i == start  = 2
                        | i == finish = 3
                        | otherwise   = x
markSF :: Int -> Int -> Int -> Square -> Square
markSF start finish i x | i == start  = 2
                        | i == finish = 3
                        | otherwise   = x
markSF start finish i x | i == start  = 2
                        | i == finish = 3
                        | otherwise   = x