1. Tikhonov, A.N. and Samarskii, A.A., Uravneniya matematicheskoi fiziki (Equations of Mathematical Physics), Moscow: Mosk. Gos. Univ., 1999.
2. Denisov, A.M., Inverse Problem for a Hyperbolic Equation with Nonlocal Boundary Condition Containing a Delay Argument, Proc. Steklov Inst. Math., 2013, vol. 280.Suppl. 1, pp. 51–58.
3. Denisov, A.M., Uniqueness of the Determination of the Nonlinear Coefficient of a System of Partial Differential Equations in the Small and in the Large, Dokl. Akad. Nauk, 1994, vol. 338, no. 4, pp. 444–447.
4. Denisov, A.M., Determination of a Nonlinear Coefficient in a Hyperbolic Equation for the Goursat Problem, J. Inverse Ill-Posed Probl., 1998, vol. 6, no. 4, pp. 327–334.
5. Cannon, J.R. and DuChateau, P., An Inverse Problem for an Unknown Source Term in a Wave Equation, SIAM J. Appl. Math., 1983, vol. 43, no. 3, pp. 553–564.