Eriksson, S.-L., and H. Orelma. “A Mean-Value Theorem for Some Eigenfunctions of the Laplace-Beltrami Operator on the Upper-Half Space”. Annales Fennici Mathematici, vol. 36, no. 1, Feb. 2011, pp. 101-10, doi:10.5186/aasfm.2011.3606.