Hyperstability of the Jensen functional equation in ultrametric spaces

In this paper, we present hyperstability results of Jensen functional equations in ultrametric Banach spaces.     

A New Variant of Wilson’s Functional Equation on Monoids

Acta Mathematica Sinica, English Series - We find on a monoid M the complex-valued solutions f, g : M → ? such that f is central and g is continuous of the functional equation $$f\left(...