BerezanskyY. M., MitropolskiyY. A., and Shkhanukov-LafishevM. K. “On a Nonlocal Problem for a Parabolic Equation”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 47, no. 6, June 1995, pp. 790–800, https://umj.imath.kiev.ua/index.php/umj/article/view/5473.