Periodic solutions of nonlinear perturbations of ϕϕ-Laplacians with possibly bounded ϕϕ

Using Leray–Schauder degree theory we obtain various existence and multiplicity results for nonlinear periodic boundary-value problems of the form (ϕ(u′))′=f(t,u,u′),u(0)−u(T)=0=u′(0)−u′(T), where ϕ:R→]−a,a[(0