@article{RM_1991_46_5_a1,
     author = {M. Ya. Zhitomirskii},
     title = {Degeneracies of differential 1-forms and {Pfaffian} structures},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     pages = {53--90},
     publisher = {mathdoc},
     volume = {46},
     number = {5},
     year = {1991},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/RM_1991_46_5_a1/}
}