1. J. Aczél, Lectures on Functional Equations and their Applications, Academic Press (New York, 1966)
2. J. Aczél and J. Dhombres, Functional Equations in Several Variables, with applications to mathematics, information theory and to the natural and social sciences, Encyclopedia of Mathematics and its Applications, vol. 31, Cambridge University Press (Cambridge, 1989)
3. Ajebbar, O., Elqorachi, E.: Solutions and stability of trigonometric functional equations on an amenable group with an involutive automorphism. Commun. Korean Math. Soc. 34, 55-82 (2019)
4. J.K. Chung, Pl. Kannappan, and C.T. Ng, A generalization of the cosine-sine functional equation on groups, Linear Algebra Appl., 66 (1985), 259-277
5. B. Ebanks, The sine addition and subtraction formulas on semigroups, Acta Math. Hungar. (to appear)