Addendum à « R. G. McLenaghan : on the validity of Huygens' principle for second order partial differential equations with four independent variables. I »
Annales de l'I.H.P. Physique théorique, Volume 26 (1977) no. 3, p. 323
@article{AIHPA_1977__26_3_323_0,
author = {McLenaghan, R. G.},
title = {Addendum \a \guillemotleft{} R. G. McLenaghan : on the validity of Huygens' principle for second order partial differential equations with four independent variables. I \guillemotright{}},
journal = {Annales de l'I.H.P. Physique th\'eorique},
publisher = {Gauthier-Villars},
volume = {26},
number = {3},
year = {1977},
pages = {323-323},
language = {en},
url = {http://www.numdam.org/item/AIHPA_1977__26_3_323_0}
}

McLenaghan, R. G. Addendum à « R. G. McLenaghan : on the validity of Huygens' principle for second order partial differential equations with four independent variables. I ». Annales de l'I.H.P. Physique théorique, Volume 26 (1977) no. 3, p. 323. http://www.numdam.org/item/AIHPA_1977__26_3_323_0/`

[1] S. Helgason, Ann. Inst. Henri Poincaré, Vol. XXI, no. 4, 1974, p. 347. | Numdam | MR 369926 | Zbl 0304.35063