1. Stability of isometries on Banach spaces;Gervirtz,1983
2. Stability of isometries;Gruber;Trans. Amer. Math. Soc.,1978
3. On the stability of the linear functional equation;Hyers,1941
4. Non-linear Perturbations of Isometries;Lindenstrauss,1985
5. A Collection of Mathematical Problems;Ulam,1961