Assanova, A.T., N.B. Iskakova, and N.T. Orumbayeva. 2018. “Well-Posedness of a Periodic Boundary Value Problem for the System of Hyperbolic Equations With Delayed Argument”. Bulletin of the Karaganda University. Mathematics Series 89 (1):8-14. https://doi.org/10.31489/2018m1/8-14.