@article{SJIM_2011_14_3_a13,
     author = {Yu. A. Chirkunov},
     title = {Friedrichs systems equivalent to the systems of wave equations},
     journal = {Sibirskij \v{z}urnal industrialʹnoj matematiki},
     pages = {132--142},
     publisher = {mathdoc},
     volume = {14},
     number = {3},
     year = {2011},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/SJIM_2011_14_3_a13/}
}