On Nonlinear Singular Perturbation Problems with Interior Nonuniformities R. O'Malley, Jr. Indiana University Mathematics Journal 1970 text pdf 10.1512/iumj.1970.19.19087 10.1512/iumj.1970.19.19087 en Indiana Univ. Math. J. 19 (1970) 1103 - 1112 state-of-the-art mathematics http://iumj.org/access/