“…Since the work of Fermi, Pasta and Ulam in the 1950s [14], there were quite a number of research works developed during the last decades on DDEs. For instance, Levi and his co-workers analyzed the condition for existence of higher symmetries for a class of DDEs [15,16], Yamilov and his coworkers [17,18] made outstanding contribution to the classification of DDEs, integrability tests and connections between integrable PDEs and DDEs [19,20] and a lot of works were developed to analyze the properties of solutions of DDEs [21][22][23][24][25][26].…”