Periodic solutions of second order nonlinear difference systems with ϕϕ-Laplacian: A variational approach

TT-periodic solutions of systems of difference equations of the form Δϕ[Δu(n−1)]=∇uF[n,u(n)]+h(n)(n∈Z) where ϕ=∇Φϕ=∇Φ, ΦΦ strictly convex, is a homeomorphism of RNRN onto the ball Ba⊂RNBa⊂RN, or of BaBa onto RNRN, are considered under various conditions upon FF and hh. The approach is variational.