TY  - JOUR
AU  - O. E. Orel
TI  - A criterion for orbital equivalence of integrable Hamiltonian systems in the vicinity of elliptic orbits. An orbital invariant in the Lagrange problem
JO  - Sbornik. Mathematics
PY  - 1997
SP  - 1085
EP  - 1105
VL  - 188
IS  - 7
UR  - http://geodesic.mathdoc.fr/item/SM_1997_188_7_a6/
LA  - en
ID  - SM_1997_188_7_a6
ER  -