@article{SM_2007_198_8_a0,
     author = {D. I. Borisov and R. R. Gadyl'shin},
     title = {The spectrum of a~self-adjoint differential},
     journal = {Sbornik. Mathematics},
     pages = {1063--1093},
     year = {2007},
     volume = {198},
     number = {8},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_2007_198_8_a0/}
}