@article{DE_1987_23_1_a6,
     author = {A. E. Evzhanov},
     title = {A lower bound for the sum of squares of fundamental functions of a second-order selfadjoint elliptic operator},
     journal = {Differencialʹnye uravneni\^a},
     pages = {62--72},
     publisher = {mathdoc},
     volume = {23},
     number = {1},
     year = {1987},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1987_23_1_a6/}
}