@article{AIHPA_1990__53_2_159_0,
     author = {M\"uller zum Hagen, H.},
     title = {Characteristic initial value problem for hyperbolic systems of second order differential equations},
     journal = {Annales de l'I.H.P. Physique th\'eorique},
     pages = {159--216},
     publisher = {Gauthier-Villars},
     volume = {53},
     number = {2},
     year = {1990},
     mrnumber = {1079777},
     zbl = {0739.35039},
     language = {en},
     url = {http://www.numdam.org/item/AIHPA_1990__53_2_159_0/}
}