@article{DAN_1983_270_4_a2,
     author = {Yu. L. Ershov},
     title = {The $\Sigma $-enumeration principle},
     journal = {Doklady Akademii Nauk},
     pages = {786--788},
     publisher = {mathdoc},
     volume = {270},
     number = {4},
     year = {1983},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1983_270_4_a2/}
}