@article{SM_1973_19_2_a7,
     author = {L. M. Martynov},
     title = {On accessible classes of groups and semigroups},
     journal = {Sbornik. Mathematics},
     pages = {231--241},
     publisher = {mathdoc},
     volume = {19},
     number = {2},
     year = {1973},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1973_19_2_a7/}
}