@article{DAN_1974_218_4_a0,
     author = {L. I. Vainerman},
     title = {Selfadjoint boundary-value problems for strongly elliptic and hyperbolic equations of second order in {Hilbert} space},
     journal = {Doklady Akademii Nauk},
     pages = {745--748},
     publisher = {mathdoc},
     volume = {218},
     number = {4},
     year = {1974},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1974_218_4_a0/}
}