@article{article37d5b9cc,
title   = {Free products of units in algebras - I: quaternion algebras},
author = {Gonçalves, Jairo Zacarias and Mandel, Arnaldo and Shirvani, Mazi},
year = {1999},
doi = {10.1006/jabr.1998.7680},
journal   = {Journal of Algebra}
}