Aguirre, Manuel A., and Emilio A. Aguirre. “Elemental Solution of the Ultrahyperbolic Equation Iterated M Times”. Nexo Scientific Journal 35, no. 04 (December 31, 2022): 867–880. Accessed July 18, 2024. https://camjol.info/index.php/NEXO/article/view/15523.