``Ahnliche'' dreidimensionale Grenzschichten Theo Geis Indiana University Mathematics Journal 1956 text pdf 10.1512/iumj.1956.5.55023 10.1512/iumj.1956.5.55023 en Indiana Univ. Math. J. 5 (1956) 643 - 686 state-of-the-art mathematics http://iumj.org/access/