1. Choquet, G., Deny, J.: Sur l’équation de convolution
$$\mu =\mu *\sigma $$
μ
=
μ
∗
σ
. C. R. Acad. Sci. Paris 250, 799–801 (1960)
2. Clifford, A.H., Preston, G.B.: The Algebraic Theory of Semigroups. Vol. I. Mathematical Surveys, vol. 7. American Mathematical Society, Providence (1961)
3. Doob, J.L., Snell, J.L., Williamson, R.E.: Application of boundary theory to sums of independent random variables. In: Olkin, I., et al. (eds.) Contributions to Probability and Statistics, pp. 182–197. Stanford University Press, Stanford (1960)
4. Kaimanovich, V.A., Vershik, A.M.: Random walks on discrete groups: boundary and entropy. Ann. Probab. 11(3), 457–490 (1983)
5. Lesokhin, M.M.: Characters of commutative semigroups. I. Izv. Vyssh. Uchebn. Zaved. Mat. 8(99), 67–74 (1970) (in Russian)