checkio([
    [1, 2, 1, 1],
    [1, 1, 4, 1],
    [1, 3, 1, 6],
    [1, 7, 2, 5]
    ]) == True

checkio([
    [7, 1, 4, 1],
    [1, 2, 5, 2],
    [3, 4, 1, 3],
    [1, 1, 8, 1]
    ]) == False

checkio([
    [2, 1, 1, 6, 1],
    [1, 3, 2, 1, 1],
    [4, 1, 1, 3, 1],
    [5, 5, 5, 5, 5],
    [1, 1, 3, 1, 1]
    ]) == True

checkio([
    [7, 1, 1, 8, 1, 1],
    [1, 1, 7, 3, 1, 5],
    [2, 3, 1, 2, 5, 1],
    [1, 1, 1, 5, 1, 4],
    [4, 6, 5, 1, 3, 1],
    [1, 1, 9, 1, 2, 1]
    ]) == True"