@article{DAN_1983_268_4_a9,
     author = {M. F. Ra\c{t}\u{a}},
     title = {Unsolvability of the problem of functional expressibility in the modal logic $\mathrm{S}4$},
     journal = {Doklady Akademii Nauk},
     pages = {814--817},
     publisher = {mathdoc},
     volume = {268},
     number = {4},
     year = {1983},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1983_268_4_a9/}
}