@article{RM_2006_61_4_a4,
     author = {P. B. Djakov and B. S. Mityagin},
     title = {Instability zones of periodic 1-dimensional {Schr\"odinger} and {Dirac} operators},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     pages = {663--766},
     publisher = {mathdoc},
     volume = {61},
     number = {4},
     year = {2006},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/RM_2006_61_4_a4/}
}