John M. Rassias, M. Arunkumar, E. Sathya, and N. Mahesh Kumar. “Generalized Ulam - Hyers Stability of on (AQQ): Additive-Quadratic-Quartic Functional Equation”. Malaya Journal of Matematik, vol. 5, no. 01, Jan. 2017, pp. 122-4, doi:10.26637/mjm501/012.