@article{DAN_1969_188_5_a9,
     author = {Z. I. Kozlova},
     title = {Certain $\Delta\Sigma$-operations whose bases are obtained by uniting the chains of the base of the original operation},
     journal = {Doklady Akademii Nauk},
     pages = {1001--1003},
     publisher = {mathdoc},
     volume = {188},
     number = {5},
     year = {1969},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1969_188_5_a9/}
}