The multiplicity of solutions in non-homogeneous boundary value problems

We use a method recently devised by Bolle to establish the existence of an infinite number of solutions for various non-homogeneous boundary value pro blems. In particular, we consider second order systems, Hamiltonian systems as well as semi-linear partial differential equations. The non-homogeneity can originate in the equation but also from the boundary conditions. The r esults are more satisfactory than those obtained by the standard "Perturbat ion from Symmetry" method that was developed - in various forms - in the ea rly eighties by Bahri-Berestycki, Struwe and Rabinowitz.