@article{SM_2007_198_4_a2,
     author = {D. B. Zot'ev},
     title = {Contact degeneracies of closed  2-forms},
     journal = {Sbornik. Mathematics},
     pages = {491--520},
     publisher = {mathdoc},
     volume = {198},
     number = {4},
     year = {2007},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_2007_198_4_a2/}
}