TY  - JOUR
AU  - L. M. Lerman
AU  - Ya. L. Umanskii
TI  - Classification of four-dimensional integrable Hamiltonian systems and Poisson actions of~$\mathbb{R}^2$ in extended neighborhoods of simple singular points.~I
JO  - Sbornik. Mathematics
PY  - 1994
SP  - 511
EP  - 542
VL  - 77
IS  - 2
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/SM_1994_77_2_a15/
LA  - en
ID  - SM_1994_77_2_a15
ER  -