Ulam stability results of functional equations in modular spaces and 2-banach spaces

Abstract
In this work, we investigate the refined stability of the additive, quartic, and quintic functional equations in modular spaces with and without the D2-condition using the direct method (Hyers method). We also examine Ulam stability in 2-Banach space using the direct method. Additionally, using a suitable counterexample, we eventually demonstrate that the stability of these equations fails in a certain case.
Description
Keywords
quartic and quintic functional equations; modular spaces; 2-Banach spaces; refined stability
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