@article{10_4153_CMB_1984_046_7,
     author = {Gon\c{c}alves, Jairo Zacarias},
     title = {Free {Subgroups} of {Units} in {Group} {Rings}},
     journal = {Canadian mathematical bulletin},
     pages = {309--312},
     year = {1984},
     volume = {27},
     number = {3},
     doi = {10.4153/CMB-1984-046-7},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-1984-046-7/}
}