Štikonas, Artūras. “A Survey on Stationary Problems, Green’s Functions and Spectrum of Sturm–Liouville Problem With Nonlocal Boundary Conditions”. Nonlinear Analysis: Modelling and Control 19, no. 3 (October 30, 2014): 301–334. Accessed April 29, 2024. https://www.journals.vu.lt/nonlinear-analysis/article/view/13638.