@article{IM2_1986_27_3_a2,
     author = {S. Z. Levendorskii},
     title = {The method of approximate spectral projection},
     journal = {Izvestiya. Mathematics },
     pages = {451--502},
     publisher = {mathdoc},
     volume = {27},
     number = {3},
     year = {1986},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_1986_27_3_a2/}
}