@article{GDZPPN002314908,
title = {Extremal Positive Semidefinite Forms.},
journal = {Mathematische Annalen},
volume = {229},
year = {1977},
pages = {1-18},
zbl = {0347.15009},
url = {http://dml.mathdoc.fr/item/GDZPPN002314908}
}
Choi, Man-Duen; Lam, Tsit-Yuen. Extremal Positive Semidefinite Forms.. Mathematische Annalen, Tome 229 (1977) pp. 1-18. http://gdmltest.u-ga.fr/item/GDZPPN002314908/