@article{SM_1995_186_2_a6,
     author = {O. E. Orel},
     title = {Rotation function for integrable problems reducing to {the~Abel} equations. {Orbital} classification of {Goryachev--Chaplygin} systems.},
     journal = {Sbornik. Mathematics},
     pages = {271--296},
     publisher = {mathdoc},
     volume = {186},
     number = {2},
     year = {1995},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1995_186_2_a6/}
}