@article{701268,
     title = {Characterization of the extremal rays of the cones of positive elements in tensor algebras},
     booktitle = {Proceedings of the 10th Winter School on Abstract Analysis},
     series = {GDML\_Books},
     publisher = {Circolo Matematico di Palermo},
     address = {Palermo},
     year = {1982},
     pages = {[135]-145},
     mrnumber = {MR0683775},
     zbl = {0522.46046},
     url = {http://dml.mathdoc.fr/item/701268}
}

Hofmann, Gerald. Characterization of the extremal rays of the cones of positive elements in tensor algebras, dans Proceedings of the 10th Winter School on Abstract Analysis, GDML_Books,  (1982), pp. [135]-145. http://gdmltest.u-ga.fr/item/701268/