@article{DAN_1979_247_5_a1,
     author = {\`E. A. Golubov and M. V. Sapir},
     title = {Varieties of finitely approximable semigroups},
     journal = {Doklady Akademii Nauk},
     pages = {1037--1041},
     publisher = {mathdoc},
     volume = {247},
     number = {5},
     year = {1979},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1979_247_5_a1/}
}