Samoilenko, V. G., and Yu. I. Samoilenko. “Asymptotic $Σ$-Solutions to Singularly perturbed Benjamin – Bona – Mahony Equation With Variable Coefficients”. Ukrains’kyi Matematychnyi Zhurnal 70, no. 2 (February 25, 2018): 236-254. Accessed October 5, 2022. http://umj.imath.kiev.ua/index.php/umj/article/view/1554.