@article{DAN_1971_197_4_a7,
     author = {V. A. Il'in and E. I. Moiseev},
     title = {On spectral decompositions corresponding to an arbitrary nonnegative selfadjoint elliptic operator of second order},
     journal = {Doklady Akademii Nauk},
     pages = {770--772},
     publisher = {mathdoc},
     volume = {197},
     number = {4},
     year = {1971},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1971_197_4_a7/}
}