Horodets’kyi, V. V., and O. V. Martynyuk. “Nonlocal Problem Multipoint in Time for the Evolutionary Equations With Pseudo-Bessel Operators With Variable Symbols”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 66, no. 2, Feb. 2014, pp. 159–175, https://umj.imath.kiev.ua/index.php/umj/article/view/2120.