@article{SM_1998_189_11_a2,
     author = {B. S. Kruglikov},
     title = {Some classification problems in four-dimensional  geometry: distributions, almost complex structures, and generalized {Monge--Ampere} equations},
     journal = {Sbornik. Mathematics},
     pages = {1643--1656},
     publisher = {mathdoc},
     volume = {189},
     number = {11},
     year = {1998},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1998_189_11_a2/}
}