@article{DAN_1970_191_5_a7,
     author = {Z. K. Litvintseva},
     title = {The complexity of certain problems for groups and semigroups},
     journal = {Doklady Akademii Nauk},
     pages = {989--992},
     publisher = {mathdoc},
     volume = {191},
     number = {5},
     year = {1970},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1970_191_5_a7/}
}