@article{AIHPA_1988__48_3_267_0,
     author = {McLenaghan, R. G. and Walton, T. F.},
     title = {An explicit determination of the non-self-adjoint wave equations on curved space-time that satisfy {Huygens'} principle. {Part} {I} : {Petrov} type {N} background space-times},
     journal = {Annales de l'I.H.P. Physique th\'eorique},
     pages = {267--280},
     publisher = {Gauthier-Villars},
     volume = {48},
     number = {3},
     year = {1988},
     mrnumber = {950268},
     zbl = {0645.53047},
     language = {en},
     url = {http://www.numdam.org/item/AIHPA_1988__48_3_267_0/}
}