by Alekseevsky, Dmitry, Dotti de Miatello, Isabel, Ferraris, Carlos
Published in Pacific journal of mathematics (01.09.1996)

by Ferraris, Carlos J.
Published in Mathematische Zeitschrift (01.10.1980)

by Druetta, Maria J., Ferraris, Carlos J.
Published in Archiv der Mathematik (01.12.1981)