@article{AA_2003_15_5_a0,
     author = {M. Sh. Birman and T. A. Suslina},
     title = {Periodic differential operators of second order. {Threshold} properties and averagings},
     journal = {Algebra i analiz},
     pages = {1--108},
     publisher = {mathdoc},
     volume = {15},
     number = {5},
     year = {2003},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AA_2003_15_5_a0/}
}