@article{GDZPPN00233089X, title = {Elementary Contractions of Gorenstein Threefolds.}, journal = {Mathematische Annalen}, volume = {280}, year = {1988}, pages = {521-526}, zbl = {0616.14003}, url = {http://dml.mathdoc.fr/item/GDZPPN00233089X} }
Cutkosky, Steven. Elementary Contractions of Gorenstein Threefolds.. Mathematische Annalen, Tome 280 (1988) pp. 521-526. http://gdmltest.u-ga.fr/item/GDZPPN00233089X/