@article{DAN_1971_199_3_a10,
     author = {Yu. G. Ol'khovskii},
     title = {On smooth relaxation operators},
     journal = {Doklady Akademii Nauk},
     pages = {548--550},
     publisher = {mathdoc},
     volume = {199},
     number = {3},
     year = {1971},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1971_199_3_a10/}
}