Skučaitė, Agnė, and Artūras Štikonas. “Zeroes and Poles of a Characteristic Function for Sturm–Liouville Problem With Nonlocal Integral Condition”. Lietuvos matematikos rinkinys 56, no. A (December 23, 2015): 95-100. Accessed October 7, 2022. https://www.journals.vu.lt/LMR/article/view/14942.