The theory of Ulam stability was initiated by a problem raised in 1940 by S. Ulam and
concerning approximate solutions to the equation of homomorphism in groups. It is
somehow connected to various other areas of investigation such as, eg, optimization and
approximation theory. Its main issue is the error that we make when replacing functions
satisfying the equation approximately with exact solutions of the equation. This article is a
survey of the published so far results on Ulam stability for functional equations in 2-normed …

Ulam stability is motivated by the following issue: how much an approximate solution of an
equation differs from the exact solutions to the equation. It is connected to some other areas
of investigation, eg, optimization, approximation theory and shadowing. In this paper, we
present and discuss the published results on such stability for functional equations in the
classes of function-taking values in 2-normed spaces. In particular, we point to several
pitfalls they contain and provide possible simple improvements to some of them. Thus we …