@article{ZNSL_1977_68_a0,
     author = {A. P. Beltiukov},
     title = {A maximal sequence of classes transformable by primitive recursion in a given class},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {3--18},
     year = {1977},
     volume = {68},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_1977_68_a0/}
}