We investigate the effect of the topology of the boundary ∂Ω and of the graph topology of the coefficient Q on the number of solutions of the nonlinear Neumann problem $(1_d)$.
Permanent address:, Department of Mathematics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, P.O.Box 71010, Wuhan 430071, P.R. China, Current address:, ECC-UNICAMP, 13083-970, Campinas, S.P. Brazil