Asymptotic Solution of Systems of Linear Ordinary Differential Equations with Discontinuous Coefficients Clive ChesterJoseph Keller Indiana University Mathematics Journal 1961 text pdf 10.1512/iumj.1961.10.10037 10.1512/iumj.1961.10.10037 en Indiana Univ. Math. J. 10 (1961) 557 - 567 state-of-the-art mathematics http://iumj.org/access/