@article{DAN_1977_233_6_a12,
     author = {V. V. Fedorchuk},
     title = {On $\pi$-sets},
     journal = {Doklady Akademii Nauk},
     pages = {1060--1063},
     publisher = {mathdoc},
     volume = {233},
     number = {6},
     year = {1977},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1977_233_6_a12/}
}