<?php
[],
[[1]],
[[1, 2], [4, 3]],
[[1, 2, 3], [8, 9, 4], [7, 6, 5]],
[[1, 2, 3, 4], [12, 13, 14, 5], [11, 16, 15, 6], [10, 9, 8, 7]],
[[1, 2, 3, 4], [10, 11, 12, 5],[9, 8, 7, 6]]
]));
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