@article{AA_1994_6_3_a1,
     author = {M. Sh. Birman and D. R. Yafaev},
     title = {The scattering matrix for a~perturbation of a~periodic {Schr\"odinger} operator by decreasing potential},
     journal = {Algebra i analiz},
     pages = {17--39},
     publisher = {mathdoc},
     volume = {6},
     number = {3},
     year = {1994},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AA_1994_6_3_a1/}
}