Sóstenes Lins Emerson Oliveira-Lima Valdenberg Silva A homological solution for the Gauss code problem in arbitrary surfaces. 506-515 2008 98 J. Comb. Theory, Ser. B 3 http://dx.doi.org/10.1016/j.jctb.2007.08.007 db/journals/jct/jctb98.html#LinsOS08