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Solution of a stability problem of Ulam. (English) Zbl 0779.47005

From the author’s summary: In our paper [J. M. Rassias, J. Approx. Th. 57, No. 3, 268-273 (1989; Zbl 0672.41027)] we solved the following Ulam Problem: “Give conditions in order for a linear mapping near an approximately linear mapping to exist” and established results involving a product of powers of norms. In this paper we state and prove a more general version of our above theorem involving a nonnegative real-valued function [S. M. Ulam, “A Collection of Mathematical Problems”, New York (1961; Zbl 0086.241); “Problems in Modern Mathematics”, New York (1964; Zbl 0137.242); “Sets, Numbers and Universes”, Cambridge, MA, (1974; Zbl 0558.00017)].

MSC:

47A05 General (adjoints, conjugates, products, inverses, domains, ranges, etc.)
47A30 Norms (inequalities, more than one norm, etc.) of linear operators
41A65 Abstract approximation theory (approximation in normed linear spaces and other abstract spaces)