An explicit determination of the Petrov type D spacetimes on which Weyl's neutrino equation and Maxwell's equations satisfy Huygens' principle R. G. McLenaghan; G. C. Williams — 1990 Annales de l'I.H.P. Physique théorique
Consequences of the validity of Huygens' principle for the conformally invariant scalar wave equation, Weyl's neutrino equation and Maxwell's equations on Petrov type II space-times J. Carminati; S. R. Czapor; R. G. McLenaghan; G. C. Williams — 1991 Annales de l'I.H.P. Physique théorique