A. Ebadian, N. Ghobadipour, I. Nikoufar & M. Eshaghi Gordji. (1970). Approximation of the Cubic Functional Equations in Lipschitz Spaces.
            <i>Analysis in Theory and Applications</i>. <i>30</i> (4).
            354-362.
         doi:10.4208/ata.2014.v30.n4.2