@article{DAN_1967_177_6_a4,
     author = {M. E. Lerner},
     title = {A maximum principle for hyperbolic equations and its application to equations of mixed type},
     journal = {Doklady Akademii Nauk},
     pages = {1269--1272},
     publisher = {mathdoc},
     volume = {177},
     number = {6},
     year = {1967},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1967_177_6_a4/}
}