@article{AL_1963_2_2_a2,
     author = {A. A. Lyapunov},
     title = {Operations on sets},
     journal = {Algebra i logika},
     pages = {47--56},
     publisher = {mathdoc},
     volume = {2},
     number = {2},
     year = {1963},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AL_1963_2_2_a2/}
}