On the Occurrence of "Vacuum States" for 2 $\times$ 2 Quasilinear Hyperbolic Conservation Laws. J. Part. Diff. Eq. [Internet]. 1995 Aug. 1 [cited 2025 Dec. 6];8(1):64-72. Available from: https://global-sci.com/index.php/jpde/article/view/14847