%0 Journal Article
%A O. E. Orel
%T A criterion for orbital equivalence of integrable Hamiltonian systems in the~vicinity of elliptic orbits. An~orbital invariant in the~Lagrange problem
%J Sbornik. Mathematics
%D 1997
%P 1085-1105
%V 188
%N 7
%I mathdoc
%U http://geodesic.mathdoc.fr/item/SM_1997_188_7_a6/
%G en
%F SM_1997_188_7_a6