@article{10_4153_CMB_2012_042_0,
     author = {Xie, BaoHua and Wang, JieYan and Jiang, YuePing},
     title = {Free {Groups} {Generated} by {Two} {Heisenberg} {Translations}},
     journal = {Canadian mathematical bulletin},
     pages = {881--889},
     year = {2013},
     volume = {56},
     number = {4},
     doi = {10.4153/CMB-2012-042-0},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-2012-042-0/}
}