@article{GDZPPN00233609X, title = {Extremal rays on higher dimensional projective varieties.}, journal = {Mathematische Annalen}, volume = {291}, year = {1991}, pages = {497-504}, zbl = {0762.14009}, url = {http://dml.mathdoc.fr/item/GDZPPN00233609X} }
Zhang, Qi. Extremal rays on higher dimensional projective varieties.. Mathematische Annalen, Tome 291 (1991) pp. 497-504. http://gdmltest.u-ga.fr/item/GDZPPN00233609X/