@article{ZNSL_1977_70_a0,
     author = {L. A. Bordag},
     title = {A gap in the energy spectrum of the one-dimensional {Dirac} operator},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {7--10},
     publisher = {mathdoc},
     volume = {70},
     year = {1977},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_1977_70_a0/}
}