@article{SM_1989_62_2_a2,
     author = {A. K. Gushchin and V. P. Mikhailov},
     title = {Comparison theorems for solutions of hyperbolic equations},
     journal = {Sbornik. Mathematics},
     pages = {349--371},
     year = {1989},
     volume = {62},
     number = {2},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1989_62_2_a2/}
}