@article{DAN_1967_172_2_a0,
     author = {I. U. Bronshtein},
     title = {Verbal subgroups of free groups},
     journal = {Doklady Akademii Nauk},
     pages = {255--257},
     publisher = {mathdoc},
     volume = {172},
     number = {2},
     year = {1967},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1967_172_2_a0/}
}