@misc{AL_1990_29_2_a0,
     title = {Yuri\u{\i} {Leonidovich} {Ershov} (on the occasion of his fiftieth               birthday)},
     journal = {Algebra i logika},
     pages = {135--138},
     publisher = {mathdoc},
     volume = {29},
     number = {2},
     year = {1990},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AL_1990_29_2_a0/}
}