[ 0, undef, 1, undef, undef, 2, 3, 4, 5, 6 ],
    [ 0, 1, 2, 3, 4, 5, 6, undef, 7, 8 ],
    [ 0, undef, 1, 2, 3, 4, 5, undef, 6, 7 ],