In this paper, we prove the existence of solutions of nonlinear boundary value problems of
arbitrary even order using the lower and upper solutions method. In particular, we point out the
fact that the existence of a pair of lower and upper solutions of a considered problem could imply
the existence of solution of another one with different boundary conditions. We consider Neumann,
Dirichlet, mixed and periodic boundary conditionsThe authors were partially supported by Xunta de Galicia (Spain), project EM2014/032 and AIE, Spain and FEDER, grant MTM2016-75140-PS
