1. 1. Ya. O. Baranetskij, P. I. Kalenyuk, "Boundary-value problems with Birkhoff regular but not strongly regular conditions for a second-order differential operator," Mat. Met. Fiz.-Mekh. Polya, 59, No. 4, 7-23 (2016)
2. English translation: J. Math. Sci., 238, No. 1, 1-21 (2019), https://doi.org/10.1007/s10958-019-04214-z
3. 2. Ya. O. Baranetskij, P. I. Kalenyuk, "Nonlocal multipoint problem with multiple spectrum for an ordinary (2n)th order differential equation," Mat. Met. Fiz.-Mekh. Polya, 60, No. 3, 32-45 (2017)
4. English translation: J. Math. Sci., 246, No. 2, 152-169 (2020), https://doi.org/10.1007/s10958-020-04727-y
5. 3. Ya. O. Baranetskij, P. I. Kalenyuk, "A non-local problem with multipoint perturbations of the boundary conditions of the Sturm-type for an ordinary differential equation of even order," Mat. Met. Fiz.-Mekh. Polya, 62, No. 1, 25-36 (2019).