Lehlou, F., Moussa, M., Roukbi, A. and Kabbaj, S. (2016) “On the superstability of the cosine and sine type functional equations”, Annales Universitatis Paedagogicae Cracoviensis Studia Mathematica, 15, pp. 113–121. Available at: https://studmath.uken.krakow.pl/article/view/13147 (Accessed: 31 October 2026).