@article{AL_1997_36_5_a1,
     author = {V. G. Bardakov},
     title = {On the width of verbal subgroups of some free constructions},
     journal = {Algebra i logika},
     pages = {494--517},
     publisher = {mathdoc},
     volume = {36},
     number = {5},
     year = {1997},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AL_1997_36_5_a1/}
}