@article{10_4153_CJM_1966_081_6,
     author = {Duke, Richard A.},
     title = {The {Genus,} {Regional} {Number,} and {Betti} {Number} of a {Graph}},
     journal = {Canadian journal of mathematics},
     pages = {817--822},
     year = {1966},
     volume = {18},
     number = {1},
     doi = {10.4153/CJM-1966-081-6},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1966-081-6/}
}