@article{DAN_1977_233_6_a5,
     author = {V. Ya. Ivrii},
     title = {Wave fronts of solutions of symmetric pseudodifferential systems},
     journal = {Doklady Akademii Nauk},
     pages = {1035--1038},
     publisher = {mathdoc},
     volume = {233},
     number = {6},
     year = {1977},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1977_233_6_a5/}
}