@article{DAN_1967_176_5_a5,
     author = {M. A. Krasnosel'skii and E. A. Livshitz},
     title = {Duality principles for boundary value problems},
     journal = {Doklady Akademii Nauk},
     pages = {999--1001},
     publisher = {mathdoc},
     volume = {176},
     number = {5},
     year = {1967},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1967_176_5_a5/}
}