The geometry of the critical set of nonlinear periodic Sturm-Liouville operators

Dan Burghelea, Nicolau C. Saldanha, Carlos Tomei

We study the critical set C of the nonlinear differential operator F(u) = -u" + f(u) defined on a Sobolev space of periodic functions H^p(S^1), p >= 1. Let R^2_{xy} \subset R^3 be…