Akkaoui, Ahmed, El FatiniMohamed, and Brahim Fadli. “A Variant of D’Alembert’s Functional Equation on Semigroups With Endomorphisms”. Annales Mathematicae Silesianae 36, no. 1 (March 22, 2022): 1-14. Accessed April 19, 2024. https://www.journals.us.edu.pl/index.php/AMSIL/article/view/13456.