Asymptotic Solution of Linear Hyperbolic Partial Differential Equations Morris Kline Indiana University Mathematics Journal 1954 text pdf 10.1512/iumj.1954.3.53016 10.1512/iumj.1954.3.53016 en Indiana Univ. Math. J. 3 (1954) 315 - 342 state-of-the-art mathematics http://iumj.org/access/