G. M. Coclite, K. H. Karlsen, S. Mishra & N. H. Risebro. (1970). A Hyperbolic-Elliptic Model of Two-Phase Flow in Porous Media — Existence of Entropy Solutions.
            <i>International Journal of Numerical Analysis and Modeling</i>. <i>9</i> (3).
            562-583.
         doi: