Grigoryan, Sh. A., et al. “EXACT PARTICULAR SOLUTIONS OF NONLINEAR KLEIN-GORDON EQUATION AND THEIR APPLICATION IN FLUID MECHANICS”. Proceedings of the YSU A: Physical and Mathematical Sciences, vol. 38, no. 3 (205), Oct. 2004, pp. 42-48, doi:10.46991/PYSU:A/2004.38.3.042.