@article{AL_1971_10_2_a2,
     author = {V. M. Kopytov},
     title = {Solvability of the occurrence problem in finitely generated},
     journal = {Algebra i logika},
     pages = {169--182},
     publisher = {mathdoc},
     volume = {10},
     number = {2},
     year = {1971},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AL_1971_10_2_a2/}
}