1. Azevedo, A. V. and Marchesin, D.,Multiple viscous profile Riemann solutions in mixed elliptic-hyperbolic models for flow in porous media, inNonlinear Evolution Equations That Change Type, eds. B. Keyfitz and M. Shearer, The IMA Volumes in Mathematics and Its Applications27, 1?17 (1990).
2. Azevedo, A. V. and Marchesin, D., private communication.
3. Bell, J. B., Trangenstein, J. A. and Shubin, G. R.,Conservation laws of mixed type describing three-phase flow in porous media, SIAM J. Appl. Math.46, 100?1017 (1986).
4. Bensoussan, A., Lions, J. L. and Papanicolau, G.,Asymptotic Analysis for Periodic Structures, North-Holland Publ. Co., Amsterdam 1978.
5. DiPerna, R. J.,Measure-valued solutions to conservation laws, Arch. Rat. Mech. Anal.88, No. 3, 223?270 (1985).