1. Aczél, J.: Problem 16. In: Report of the Twenty-Ninth International Symposium on Functional Equations. Aequationes Mathematicae, vol. 43, pp. 299 (1992)
2. Bahyrycz, A.: The characterization of the indicator plurality function. Rocznik Nauk.-Dydakt. WSP w Krakowie. Prace Matematyczne XV, 15–35 (1998)
3. Bahyrycz, A.: On the problem concerning the indicator plurality function. Opusc. Math. 21, 11–30 (2001)
4. Bahyrycz, A.: On sets associated to conditional equation of exponential function. Ann. Acad. Pedagog. Crac. Stud. Math. 6, 19–33 (2007)
5. Bahyrycz, A.: On systems of equations with unknown multifunctions related to the plurality function. Ann. Univ. Paedagog. Crac. Stud. Math. 9, 133–142 (2010)