We study the existence of multiple solutions for the problem
and we show that at least one of them is sign changing. Here Ω is a bounded domain in ℝ
with N ⩾ 5 whose boundary is of class C
ν is the outward normal derivative, and f ∈ L
N/2(Ω) whose L
2N/(N+2)(Ω) norm is sufficiently small.