@article{ND_2014_10_1_a6,
     author = {Gleb E. Smirnov},
     title = {Focus-focus singularities in classical mechanics},
     journal = {Russian journal of nonlinear dynamics},
     pages = {101--112},
     publisher = {mathdoc},
     volume = {10},
     number = {1},
     year = {2014},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ND_2014_10_1_a6/}
}