BlackmoreD., PrykarpatskyA. K., PrykarpatskyY. A., & SamoilenkoA. M. (2018). Theory of multidimensional Delsarte – Lions transmutation operators. I. Ukrains’kyi Matematychnyi Zhurnal, 70(12), 1660-1695. Retrieved from https://umj.imath.kiev.ua/index.php/umj/article/view/1667