Ryuhei Uehara Seinosuke Toda Takayuki Nagoya Graph isomorphism completeness for chordal bipartite graphs and strongly chordal graphs. 479-482 2005 145 Discrete Applied Mathematics 3 http://dx.doi.org/10.1016/j.dam.2004.06.008 db/journals/dam/dam145.html#UeharaTN05