Gasanenko, V. A. “Complete Asymptotic Decomposition of the Sojourn Probability of a Diffusion Process in Thin Domains With Moving Boundaries”. Ukrains’kyi Matematychnyi Zhurnal, vol. 51, no. 9, Sept. 1999, pp. 1155–1164, https://umj.imath.kiev.ua/index.php/umj/article/view/4711.