%0 Journal Article
%A McLenaghan, R. G.
%T On the validity of Huygens' principle for second order partial differential equations with four independent variables. Part I : derivation of necessary conditions
%J Annales de l'institut Henri Poincaré. Section A, Physique Théorique
%D 1974
%P 153-188
%V 20
%N 2
%I Gauthier-Villars
%U http://www.numdam.org/item/AIHPA_1974__20_2_153_0/
%G en
%F AIHPA_1974__20_2_153_0