hard2 :: Puzzle
hard2 = [
    0, 0, 1, 0, 0, 4, 0, 0, 0,
    0, 0, 0, 0, 6, 0, 3, 0, 5,
    0, 0, 0, 9, 0, 0, 0, 0, 0,
    8, 0, 0, 0, 0, 0, 7, 0, 3,
    0, 0, 0, 0, 0, 0, 0, 2, 8,
    5, 0, 0, 0, 7, 0, 6, 0, 0,
    3, 0, 0, 0, 8, 0, 0, 0, 6,
    0, 0, 9, 2, 0, 0, 0, 0, 0,
    0, 4, 0, 0, 0, 1, 0, 0, 0 ]
hard2 :: Puzzle
hard2 = [
    0, 0, 1, 0, 0, 4, 0, 0, 0,
    0, 0, 0, 0, 6, 0, 3, 0, 5,
    0, 0, 0, 9, 0, 0, 0, 0, 0,
    8, 0, 0, 0, 0, 0, 7, 0, 3,
    0, 0, 0, 0, 0, 0, 0, 2, 8,
    5, 0, 0, 0, 7, 0, 6, 0, 0,
    3, 0, 0, 0, 8, 0, 0, 0, 6,
    0, 0, 9, 2, 0, 0, 0, 0, 0,
    0, 4, 0, 0, 0, 1, 0, 0, 0 ]
hard2 = [
    0, 0, 1, 0, 0, 4, 0, 0, 0,
    0, 0, 0, 0, 6, 0, 3, 0, 5,
    0, 0, 0, 9, 0, 0, 0, 0, 0,
    8, 0, 0, 0, 0, 0, 7, 0, 3,
    0, 0, 0, 0, 0, 0, 0, 2, 8,
    5, 0, 0, 0, 7, 0, 6, 0, 0,
    3, 0, 0, 0, 8, 0, 0, 0, 6,
    0, 0, 9, 2, 0, 0, 0, 0, 0,
    0, 4, 0, 0, 0, 1, 0, 0, 0 ]