@article{MMO_1970_21_a6,
     author = {G. I. \`Eskin},
     title = {A conjugacy problem for equations of principal type with two independent variables},
     journal = {Trudy Moskovskogo matemati\v{c}eskogo ob\^{s}estva},
     pages = {245--292},
     publisher = {mathdoc},
     volume = {21},
     year = {1970},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MMO_1970_21_a6/}
}