@article{DAN_1964_158_3_a0,
     author = {G. P. Gavrilov},
     title = {On the cardinality of sets of closed classes of finite height in $P_{\aleph_0}$},
     journal = {Doklady Akademii Nauk},
     pages = {503--506},
     publisher = {mathdoc},
     volume = {158},
     number = {3},
     year = {1964},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1964_158_3_a0/}
}