1. 1. N. I. Bilusyak, L. I. Komarnyts'ka, B. I. Ptashnyk, "Dirichlet-type problems for systems of partial differential equations unresolved with respect to the highest time derivative," Ukr. Mat. Zh., 54, No. 12, 1592-1602 (2002)
2. English translation: Ukr. Math. J., 54, No. 12, 1930-1942 (2002), https://doi.org/10.1023/A:1024065029561
3. 2. I. O. Bobyk, M. M. Symotyuk, "Problem with two multiple points of interpolation for linear factorized partial differential equations," Visn. Nats. Univ. "L'viv. Politekhn.", Ser. Fiz.-Mat. Nauky, No. 687, 11-19 (2010).
4. 3. P. I. Kalenyuk, I. V. Kohut, Z. M. Nytrebych, "An investigation into a problem with homogeneous local two-point conditions for a homogeneous system of partial differential equations," Mat. Met. Fiz.-Mekh. Polya, 52, No. 4, 7-17 (2009)
5. English translation: J. Math. Sci., 174, No. 2, 121-135 (2011), https://doi.org/10.1007/s10958-011-0285-y