Bandyrskii, B., I. Lazurchak, V. Makarov, and M. Sapagovas. 2006. “Eigenvalue Problem for the Second Order Differential Equation With Nonlocal”. Nonlinear Analysis: Modelling and Control 11 (1): 13-32. https://doi.org/10.15388/NA.2006.11.1.14762.