@article{DAN_1975_222_2_a5,
     author = {I. I. Parovichenko},
     title = {On the commutativity of $\delta s$-operations},
     journal = {Doklady Akademii Nauk},
     pages = {284--287},
     publisher = {mathdoc},
     volume = {222},
     number = {2},
     year = {1975},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1975_222_2_a5/}
}