Robert Ganian Petr Hlinený Joachim Kneis Daniel Meister Jan Obdrzálek Peter Rossmanith Somnath Sikdar Are There Any Good Digraph Width Measures? 135-146 2010 IPEC http://dx.doi.org/10.1007/978-3-642-17493-3_14 conf/iwpec/2010 db/conf/iwpec/ipec2010.html#GanianHKMORS10