@article{VTGU_2012_1_a1,
     author = {S. Y. Grinshpon and M. M. Nikolskaya},
     title = {Proper fully invariant subgroups of torsion free groups isomorphic to the group},
     journal = {Vestnik Tomskogo gosudarstvennogo universiteta. Matematika i mehanika},
     pages = {11--15},
     year = {2012},
     number = {1},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/VTGU_2012_1_a1/}
}