YAZID, Fares, et al. “Global Nonexistence of Solutions to System of Klein-Gordon Equations With Degenerate Damping and Strong Source Terms in Viscoelasticity”. Studia Universitatis Babeș-Bolyai Mathematica, vol. 67, no. 3, Sept. 2022, pp. 563–578, doi:10.24193/subbmath.2022.3.08.