@article{DAN_1988_298_3_a4,
     author = {V. A. Derkach and M. M. Malamud and \`E. R. Tsekanovskii},
     title = {Sectorial extensions of a positive operator, and the},
     journal = {Doklady Akademii Nauk},
     pages = {537--541},
     publisher = {mathdoc},
     volume = {298},
     number = {3},
     year = {1988},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1988_298_3_a4/}
}