“…In the sequel, we would like to mention some important works on this subject. Regarding the wellposedness of problem (1.1), the analytic case is rather known in general dimensions, as, for instance, [8], [9] and [25]. In what concerns solutions for (1.1) lying in Sobolev spaces and, as far as we know, the results presented in the literature are only local in time, as, for example, [1] and [24].…”