Cj. Zhu, RIEMANN PROBLEM FOR A CLASS OF 2X2 HYPERBOLIC CONSERVATION-LAWS, Proceedings of the Royal Society of Edinburgh. Section A. Mathematics, 126, 1996, pp. 719-724
In this paper we prove the global existence of the solutions of the Ri
emann problem for a class of 2 x 2 hyperbolic conservation laws, which
is neither necessarily strictly hyperbolic nor necessarily genuinely
nonlinear.