@article{DAN_1985_283_6_a2,
     author = {I. K. Daugavet},
     title = {Causal extension of operators},
     journal = {Doklady Akademii Nauk},
     pages = {1299--1301},
     publisher = {mathdoc},
     volume = {283},
     number = {6},
     year = {1985},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1985_283_6_a2/}
}