@article{10_4153_CMB_1986_049_x,
     author = {Gon\c{c}alves, Jairo Zacarias},
     title = {Free {Subgroups} and the {Residual} {Nilpotence} of the {Group} of {Units} of {Modular} and {p-Adic} {Group} {Rings}},
     journal = {Canadian mathematical bulletin},
     pages = {321--328},
     year = {1986},
     volume = {29},
     number = {3},
     doi = {10.4153/CMB-1986-049-x},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-1986-049-x/}
}