Roman, Svetlana, and Artūras Štikonas. “The Properties of Green’s Functions for One Stationary Problem With Nonlocal Boundary Conditions”. Lietuvos Matematikos Rinkinys, vol. 50, no. proc. LMS, Oct. 2009, pp. 340–344, https://doi.org/10.15388/LMR.2009.14661.