 the deepest child reachable from some parent at level
 0. It implements a layout technique as described by
 K. Sugiyama, S. Tagawa, and M. Toda. in "Methods for
 visual understanding of hierarchical systems", IEEE
 Transactions on Systems, Man and Cybernetics,
 SMC-11(2):109-125, Feb. 1981.
 <p>There have been a few modifications made, however.
 The crossings function is changed as it was non-linear
 in time complexity. Furthermore, we don't have any
 interconnection matrices for each level, instead we
 ju