1. A Collection of Mathematical Problems;Ulam,1960
2. Problems in Modern Mathematics;Ulam,1964
3. On the stability of the linear functional equation;Hyers;Proc. Natl. Acad. Sci. USA,1941
4. Ulam Stability of Operators;Brzdęk,2018
5. Hyers–Ulam–Rassias Stability of Functional Equations in Nonlinear Analysis;Jung,2011