@article{10_1017_S0017089500003268,
     author = {Choo, Koo-Guan},
     title = {Grothendieck groups of twisted free associative algebras},
     journal = {Glasgow mathematical journal},
     pages = {193--196},
     year = {1977},
     volume = {18},
     number = {2},
     doi = {10.1017/S0017089500003268},
     url = {http://geodesic.mathdoc.fr/articles/10.1017/S0017089500003268/}
}