“…Therefore, the aim of the present work is to find all possible Lie symmetries, which Equation (1) can admit depending on the function triplets (K, D, F), i.e., to solve the so-called group classification problem, which was formulated and solved for a class of nonlinear heat equations in the pioneering work by Ovsiannikov in 1959 [20] and now is the core stone of modern group analysis [21,22]. This problem for the second-order wave equation was probably first solved by Barone et al in [23] and subsequently was extended to other general forms by many authors in the last two decades [2,[24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43], but were all limited to second-order cases.…”