@article{IVM_1999_11_a0,
     author = {U. D. Bekbaev},
     title = {Equivalence and invariants of second-order linear partial differential equations in two variables under a~change of variables},
     journal = {Izvesti\^a vys\v{s}ih u\v{c}ebnyh zavedenij. Matematika},
     pages = {3--10},
     year = {1999},
     number = {11},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/IVM_1999_11_a0/}
}