@article{DAN_1965_161_5_a5,
     author = {B. V. Popov},
     title = {Semigroups of transformations of rank not exceeding two},
     journal = {Doklady Akademii Nauk},
     pages = {1019--1022},
     publisher = {mathdoc},
     volume = {161},
     number = {5},
     year = {1965},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1965_161_5_a5/}
}