@article{DAN_1978_242_6_a4,
     author = {S. M. Ponomarev},
     title = {On the {Tricomi} problem for a system of equations of mixed type in the plane},
     journal = {Doklady Akademii Nauk},
     pages = {1256--1257},
     publisher = {mathdoc},
     volume = {242},
     number = {6},
     year = {1978},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1978_242_6_a4/}
}