@article{LJM_1999_4_a6,
     author = {O. P. Tchij},
     title = {Contact geometry of hyperbolic {Monge--Amp\`ere} equations},
     journal = {Lobachevskii journal of mathematics},
     pages = {109--162},
     publisher = {mathdoc},
     volume = {4},
     year = {1999},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/LJM_1999_4_a6/}
}