Complete Integrability and Perturbation of a Nonlinear Dirichlet Problem, II Melvyn BergerP. Church Indiana University Mathematics Journal 1980 text pdf 10.1512/iumj.1980.29.29052 10.1512/iumj.1980.29.29052 en Indiana Univ. Math. J. 29 (1980) 715 - 735 state-of-the-art mathematics http://iumj.org/access/