@article{DAN_1958_120_2_a4,
     author = {A. I. Mal'tsev},
     title = {On certain classes of models},
     journal = {Doklady Akademii Nauk},
     pages = {245--248},
     publisher = {mathdoc},
     volume = {120},
     number = {2},
     year = {1958},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1958_120_2_a4/}
}