We obtain, under weaker assumptions, a result of Dancer, Lazer-McKenna on the existence of at least three solutions for some elliptic problems with jumping nonlinearities by means of simple variational tools.
A. M. Micheletti. A. Pistoia. "A variational viewpoint on the existence of three solutions for some nonlinear elliptic problems." Differential Integral Equations 9 (5) 1029 - 1042, 1996. https://doi.org/10.57262/die/1367871529