Horban’N. V., and StanzhitskiiA. N. “Global Attractor for the Autonomous Wave Equation in <i>R<sub>n </sub></i&gt; With Continuous Nonlinearity”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 60, no. 2, Feb. 2008, pp. 260–267, https://umj.imath.kiev.ua/index.php/umj/article/view/3154.