@article{DAN_1974_218_2_a14,
     author = {S. V. Yablonskii},
     title = {The structure of the upper neighborhood for predicate-describable classes in $P_k$},
     journal = {Doklady Akademii Nauk},
     pages = {304--307},
     publisher = {mathdoc},
     volume = {218},
     number = {2},
     year = {1974},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1974_218_2_a14/}
}