The analogues of advanced and retarded fundamental solutions for ultrahyperbolic equation

We deal with the ultrahyperbolic equation in ℝ
^d
× ℝ
ⁿ
. Our goal is to construct its fundamental solutions that satisfy a certain support condition. In the particular case n = 1, they coincide with either the advanced or the retarded fundamental solution of the wave equation. Such fundamental solutions provide Volterra type transformations which can be utilized in the study of perturbed ultrahyperbolic equations.