@article{AL_1969_8_5_a1,
     author = {Yu. L. Ershov},
     title = {Hyperhypersimple $m$-degrees},
     journal = {Algebra i logika},
     pages = {523--552},
     publisher = {mathdoc},
     volume = {8},
     number = {5},
     year = {1969},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AL_1969_8_5_a1/}
}