ZadorozhnaN. M., Mel’nykO. M., and PtashnikB. I. 1994. “Nonlocal Boundary-Value Problem for Parabolic Equations”. Ukrains’kyi Matematychnyi Zhurnal 46 (12), 1621–1626. https://umj.imath.kiev.ua/index.php/umj/article/view/5573.