Pascale Kuntz Bruno Pinaud Rémi Lehn Minimizing crossings in hierarchical digraphs with a hybridized genetic algorithm. 23-36 2006 12 J. Heuristics 1-2 http://dx.doi.org/10.1007/s10732-006-4296-7 db/journals/heuristics/heuristics12.html#KuntzPL06