Existence of multiple solutions of a two-point boundary value problem at resonance (Q1386869)

Using critical point theory, and in particular Morse critical groups, the authors give new sufficient conditions for the existence of multiple solutions to the two-point boundary value problem \[ -u''= n^2u+ g(t,u),\quad u(0)= u(\pi)= 0, \] when \(n\) is a positive integer and \(g\) is not necessarily bounded.