@article{RM_1979_34_3_a6,
     author = {V. I. Feigin},
     title = {Estimates of the length of gaps in the spectrum of a~first-order system},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     pages = {198--199},
     publisher = {mathdoc},
     volume = {34},
     number = {3},
     year = {1979},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/RM_1979_34_3_a6/}
}