@article{MZM_1972_11_4_a13,
     author = {L. A. Skornyakov},
     title = {Hall varieites of semigroups},
     journal = {Matemati\v{c}eskie zametki},
     pages = {463--470},
     publisher = {mathdoc},
     volume = {11},
     number = {4},
     year = {1972},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1972_11_4_a13/}
}