“…Using the multi-scale invariant theory, the authors proved that the solution of (1.6) for small values of the parameter ε converges to a two-dimensional invariant manifold. It is also necessary to mention the results in [2] and [9], in which the authors investigated the unique solvability of nonlinear wave equations with nonlocal terms u(0, t), u(1, t) and u(η 1 , t), • • • , u(η q , t) respectively, where 0…”