Minimal Imbeddings and the Genus of a Graph J. Youngs Indiana University Mathematics Journal 1963 text pdf 10.1512/iumj.1963.12.12021 10.1512/iumj.1963.12.12021 en Indiana Univ. Math. J. 12 (1963) 303 - 315 state-of-the-art mathematics http://iumj.org/access/