Kata

You get some nested lists. Keeping the original structures, sort only elements (integers) inside of the lists. In other words, sorting the intergers only by swapping their positions.

Example
Input   : [[[2, 1], [4, 3]], [[6, 5], [8, 7]]]
Output  : [[[1, 2], [3, 4]], [[5, 6], [7, 8]]]

Note: The structures of the lists are regular (symmetrical) and their depths are 3.