Atsuhiro Nakamoto Seiya Negami Katsuhiro Ota Jozef Sirán Planar triangulations which quadrangulate other surfaces. 817-833 2004 25 Eur. J. Comb. 6 http://dx.doi.org/10.1016/j.ejc.2003.05.003 db/journals/ejc/ejc25.html#NakamotoNOS04