@article{ZNSL_1971_20_a20,
     author = {R. I. Freidson},
     title = {Regular approximations to the recursive predicates},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {220--233},
     year = {1971},
     volume = {20},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_1971_20_a20/}
}