... equation,” Proceedings of the National Academy of Sciences of the United States of America, vol. 27, no. 4, pp. 222–224, 1941.2 T. Aoki, “On the stability of the linear transformation in Banach ... of Functional Equations in Mathematical Analysis, HadronicPress, Palm Harbor, Fla, USA, 2001.16 G. L. Forti, “Comments on the core of the direct method for proving Hyers-Ulam stability of ... or to the books 13–15see also the recent articles of Forti 16, 17, for supplementary details.On the other hand, in 18–25, a fixed point method was proposed, by showing that manytheorems...