KadankovV. F., and KadankovaT. V. “Two-Boundary Problems for a Poisson Process With Exponentially Distributed Component”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 58, no. 7, July 2006, pp. 922–953, https://umj.imath.kiev.ua/index.php/umj/article/view/3506.