@article{04009334, title = {Graphs and projective planes in 3-manifolds.}, journal = {International Journal of Mathematics and Mathematical Sciences}, volume = {9}, year = {1986}, pages = {551-560}, doi = {10.1155/S0161171286000698}, zbl = {0622.57007}, language = {en}, url = {http://dml.mathdoc.fr/item/04009334} }
Heil, Wolfgang; Negami, Seiya. Graphs and projective planes in 3-manifolds.. International Journal of Mathematics and Mathematical Sciences, Tome 9 (1986) pp. 551-560. doi : 10.1155/S0161171286000698. http://gdmltest.u-ga.fr/item/04009334/