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@article{DAN_1970_190_4_a8, author = {A. A. Lyapunov}, title = {The covering of $A$-sets, and multiple separability}, journal = {Doklady Akademii Nauk}, pages = {775--776}, publisher = {mathdoc}, volume = {190}, number = {4}, year = {1970}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/DAN_1970_190_4_a8/} }
A. A. Lyapunov. The covering of $A$-sets, and multiple separability. Doklady Akademii Nauk, Tome 190 (1970) no. 4, pp. 775-776. http://geodesic.mathdoc.fr/item/DAN_1970_190_4_a8/