@article{SM_1992_71_2_a10,
     author = {A. P. Buslaev and V. M. Tikhomirov},
     title = {Spectra of nonlinear differential equations and widths of {Sobolev} classes},
     journal = {Sbornik. Mathematics},
     pages = {427--446},
     publisher = {mathdoc},
     volume = {71},
     number = {2},
     year = {1992},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1992_71_2_a10/}
}