%0 Journal Article
%A M. Sh. Birman
%A A. Laptev
%A T. A. Suslina
%T The discrete spectrum of a~two-dimensional second-order periodic elliptic operator perturbed by a~decreasing potential.~I. A~semi-infinite gap
%J Algebra i analiz
%D 2000
%P 36-78
%V 12
%N 4
%I mathdoc
%U http://geodesic.mathdoc.fr/item/AA_2000_12_4_a2/
%G ru
%F AA_2000_12_4_a2