@article{AL_2011_50_6_a4,
     author = {M. Manat and A. Sorbi},
     title = {Positive undecidable numberings in the {Ershov} hierarchy},
     journal = {Algebra i logika},
     pages = {759--780},
     publisher = {mathdoc},
     volume = {50},
     number = {6},
     year = {2011},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AL_2011_50_6_a4/}
}