1. Adams, R.: Sobolev space. New York: Academic Press 1975
2. Bardos, C., Rauch, J.: Maximally positive boundary value problems as limits of singular perturbation problems. Trans. Am. Math. Soc.270, 377–408 (1982)
3. Chen Shuxing: On the initial-boundary value problems for quasilinear symmetric hyperbolic systems with characteristic boundary (in chinese). Chinese Ann. Math.3, 223–232 (1982)
4. Hardy, G.H., Littlewood, J.E., Pólya, G.: Inequalities. Cambridge: Cambridge University Press 1934
5. Hörmander, L.: Linear partial differential operator. Berlin, Heidelberg, New York: Springer 1963