LEHLOU, F.; MOUSSA, M.; ROUKBI, A.; KABBAJ, S. On the superstability of the cosine and sine type functional equations. Annales Universitatis Paedagogicae Cracoviensis Studia Mathematica, [S. l.], v. 15, p. 113–121, 2016. Disponível em: https://studmath.uken.krakow.pl/article/view/13147. Acesso em: 31 oct. 2026.