Horban’, N. V., and A. N. Stanzhitskii. 2008. “Global Attractor for the Autonomous Wave Equation in <i>R<sub>n </sub></i&gt; With Continuous Nonlinearity”. Ukrains’kyi Matematychnyi Zhurnal 60 (2), 260–267. https://umj.imath.kiev.ua/index.php/umj/article/view/3154.