Vedat Suat Ertürk,  Zaid M. Odibat & Shaher Momani. (1970). The Multi-Step Differential Transform Method and Its Application to Determine the Solutions of Non-Linear Oscillators.
            <i>Advances in Applied Mathematics and Mechanics</i>. <i>4</i> (4).
            422-438.
         doi:10.4208/aamm.10-m1138