The Bifurcation of Periodic Solutions of the Nonlinear Telegraph Equation and Infinite-Dimensional Singularity Theory Melvyn BergerGuozhang Sun Indiana University Mathematics Journal 1993 text pdf 10.1512/iumj.1993.42.42052 10.1512/iumj.1993.42.42052 en Indiana Univ. Math. J. 42 (1993) 1121 - 1147 state-of-the-art mathematics http://iumj.org/access/