Ustilko, E. V. .; Lomovtsev, F. E. . Matching Conditions for Values of Characteristic Oblique Derivative at the End of a String, Initial Data and Right-Hand Side of the Wave Equation. Журнал Белорусского государственного университета. Математика. Информатика 2020, No. 1, 30-37. https://doi.org/10.33581/2520-6508-2020-1-30-37.