Gusak, D. V. “Behavior of Risk Processes With Random Premiums After Ruin and a Multivariate Ruin Function”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 59, no. 11, Nov. 2007, pp. 1473–1484, https://umj.imath.kiev.ua/index.php/umj/article/view/3405.