... approximation of solutions for a class of nonlinear impulsivefunctional differential equations with anti-periodic boundary conditions,” Nonlinear Analysis: Theory,Methods & Applications, vol. 69, ... Obviously, ϕis continuous.Lemma 2.4. If u ∈ X is a critical point of the functional ϕ,thenu is a classical solution of IBVP2.1.4 Boundary Value ProblemsObviously, the solutions of IBVP ... “Variational methods to Sturm-Liouville boundary value problem for impulsivedifferential equations,” Nonlinear Analysis: Theory, Methods & Applications. In press.6 Boundary Value ProblemsProof....