LagnoV. I., and FushchichV. I. “Linear and Nonlinear Representations of Galilei Groups in Two-Dimensional Space-Time”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 50, no. 3, Mar. 1998, pp. 414-23, https://umj.imath.kiev.ua/index.php/umj/article/view/4941.