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
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/SM_1997_188_7_a6/
LA  - en
ID  - SM_1997_188_7_a6
ER  -