References
- [1] 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, 31, Cambridge University Press, Cambridge, 1989.
- [2] B. Ebanks, The cosine and sine addition and subtraction formulas on semigroups, Acta Math. Hungar. 165 (2021), no. 2, 337–354.
- [3] B. Ebanks, Around the sine addition law and d’Alembert’s equation on semigroups, Results Math. 77 (2022), no. 1, Paper No. 11, 14 pp.10.1007/s00025-021-01548-6
- [4] B. Ebanks and H. Stetkær, d’Alembert’s other functional equation on monoids with an involution, Aequationes Math. 89 (2015), no. 1, 187–206.
- [5] H. Stetkær, Functional Equations on Groups, World Scientific, Singapore, 2013.10.1142/8830
- [6] H. Stetkær, Extensions of the sine addition law on groups, Aequationes Math. 93 (2019), no. 2, 467–484.
- [7] H. Stetkær, Homomorphisms of product semigroups, Results Math. 77 (2022), no. 2, Paper No. 60, 21 pp.10.1007/s00025-022-01603-w
- [8] W.H. Wilson, On certain related functional equations, Bull. Amer. Math. Soc. 26 (1920), no. 7, 300–312.