“…[3], [5], [7], [8], [11], [12], [13], [17], [18], [14], [15], [16], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [31], [33], [35] and the references therein. When the initial data (v 0 (x), u 0 (x), s 0 (x)) is a small perturbation of a nonvacuum constant state, i.e., v − = v + > 0, u − = u + , s − = s + , satisfactory results have been obtained; cf.…”