[[[0, 0], [0, 1], [0, 2], [0, 3], [0, 4], [0, 5]], [[1, 0], [1, 1], [1, 2],   [1, 3], [1, 4], [1, 5]], [[2, 0], [2, 1], [2, 2], [2, 3], [2, 4], [2, 5]], [[3, 0], [3, 1], [3, 2], [3, 3], [3, 4], [3, 5]], [[4, 0], [4, 1], [4, 2], [4, 3], [4, 4], [4, 5]], [[5, 0], [5, 1], [5, 2], [5, 3], [5, 4], [5, 5]]]

[[0,0], [5,1], [5,4]...]

a = [[[0, 0], [0, 1], [0, 2], [0, 3], [0, 4], [0, 5]], [[1, 0], [1, 1], [1, 2],   [1, 3], [1, 4], [1, 5]], [[2, 0], [2, 1], [2, 2], [2, 3], [2, 4], [2, 5]], [[3, 0], [3, 1], [3, 2], [3, 3], [3, 4], [3, 5]], [[4, 0], [4, 1], [4, 2], [4, 3], [4, 4], [4, 5]], [[5, 0], [5, 1], [5, 2], [5, 3], [5, 4], [5, 5]]]

a.flatten(1)
>[[0, 0], [0, 1], [0, 2], [0, 3], [0, 4], [0, 5], [1, 0], [1, 1], [1, 2], [1, 3], [1, 4], [1, 5], [2, 0], [2, 1], [2, 2], [2, 3], [2, 4], [2, 5], [3, 0], [3, 1], [3, 2], [3, 3], [3, 4], [3, 5], [4, 0], [4, 1], [4, 2], [4, 3], [4, 4], [4, 5], [5, 0], [5, 1], [5, 2], [5, 3], [5, 4], [5, 5]]