Pečiulytė, Sigita, and Artūras Štikonas. 2007. “On Positive Eigenfunctions of Sturm‐Liouville Problem With Nonlocal two‐point Boundary Condition”. Mathematical Modelling and Analysis 12 (2):215-26. https://doi.org/10.3846/1392-6292.2007.12.215-226.