@incollection{AST_2003__284__265_0,
     author = {Rauch, Jeffrey},
     title = {Group velocity at smooth points of hyperbolic characteristic varieties},
     booktitle = {Autour de l'analyse microlocale - Volume en l'honneur de Jean-Michel Bony},
     editor = {Lebeau Gilles},
     series = {Ast\'erisque},
     pages = {265--269},
     year = {2003},
     publisher = {Soci\'et\'e math\'ematique de France},
     number = {284},
     mrnumber = {2003423},
     zbl = {1051.35039},
     language = {en},
     url = {https://www.numdam.org/item/AST_2003__284__265_0/}
}