2 - Variable AQCQ - Functional equation

In this paper, the authors obtain the general solution and generalized Ulam - Hyers stability of a 2 - variable AQCQ functional equation \begin{align*} g(x+2y, u+2v)+g(x-2y, u-2v)& = 4[g(x+y, u+v) + g(x-y, u-v)]- 6g(x,u)\notag\\ &~~+g(2y,2v)+g(-2y,-2v)-4g(y,v)-4g(-y,-v) \end{align*} using Hyers direct method. Counter examples for non stability is also discussed.