1. A. V. Bitsadze, “On structural properties of solutions of hyperbolic systems of partial differential equations of the first order,” Mat. Model. 6 (6), 22–31 (1994).
2. T. V. Chekmarev, “Formulas for solution of the Goursat problem for a linear system of partial differential equations,” Differ. Uravn. 18 (9), 1614–1622 (1982).
3. T. V. Chekmarev, Systems of Equations of Mixed Type (Nizhegorod. Gos. Tekh. Univ., Nizhny Novgorod, 1995) [in Russian].
4. I. E. Pleshchinskaya, “The equivalence of some classes of first-order elliptic and hyperbolic systems and second-order partial differential equations,” Differ. Uravn. 23 (9), 1634–1637 (1987).
5. R. K. Romanovskii, “On Riemann matrices of the first and second kind,” Math. USSR-Sb. 55 (2), 485–492 (1985). https://doi.org/10.1070/SM1986v055n02ABEH003016