Bayoud, M., et al. “Global Nonexistence of Solutions for a System of Nonlinear Viscoelastic Wave Equations With Degenerate Damping and Source Terms”. Ukrains’kyi Matematychnyi Zhurnal, vol. 65, no. 5, May 2013, pp. 654–669, https://umj.imath.kiev.ua/index.php/umj/article/view/2449.