On the Elementary Solution for the Partial Differential Operator $\circledcirc_c^{k}$ Related to the Wave Equation. Eur. J. Pure Appl. Math. [Internet]. 2018 Apr. 27 [cited 2024 May 2];11(2):390-9. Available from: https://www.ejpam.com/index.php/ejpam/article/view/3223