[1] ANTONI J., ŠALÁT T.: On the A-continuity of real functions. Acta Math. Univ. Comenian. 39, 1980, 159-164. MR 0619271 | Zbl 0519.40006

[2] Problem 4216 1946. 470 Amer. Math. Monthly. Propesed H. Robins. Solution by R. c. Buck, Amer, Math. Monthly 55, 1948, 36.

[3] MORRIS S. A.: Pontriagin duality and the structure of localy compact Abelian groups. (in Russian, Mir, Moscow 1980). MR 0602954

[4] POSNER E. C: Summability-preserving functions. Proc. Amer. Math. Soc. 12, 1961, 73-76. MR 0121591 | Zbl 0097.04602

[5] ACZEL J.: Vorlesungen über Functiolnalgleichungen und ihre Anwendungen. VEB Deutscher Verlag der Wissenschaften, Berlin 1661. MR 0124647