@article{DM_2002_14_2_a8,
     author = {M. F. Ra\c{t}\u{a}},
     title = {A formal reduction of the general problem of the expressibility of formulas in the {G\"odel-L\"ob} provability logic},
     journal = {Diskretnaya Matematika},
     pages = {95--106},
     publisher = {mathdoc},
     volume = {14},
     number = {2},
     year = {2002},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DM_2002_14_2_a8/}
}