In this paper we explicitly calculate fundamental solutions for the Tricomi operator, relative to an arbitrary point in the plane, and show that all such fundamental solutions originate from the hypergeometric function F(1/6,1/6;1;ζ)$ that is obtained when we look for homogeneous solutions to the reduced hyperbolic Tricomi equation.
"Fundamental solutions for the Tricomi operator, II." Duke Math. J. 111 (3) 561 - 584, 15 February 2002. https://doi.org/10.1215/S0012-7094-02-11137-5