“…There has been increasing interest in the investigation for boundary-value problems of nonlinear impulsive differential equations during the past few years and many literature have been published about the existence of solutions for first-order or second-order impulsive differential equations, see [1--10] and the references therein. There are some common techniques to approach these problems: the fixed point theorems [1,6,8,10]; the method of upper and lower solutions [3--5, 9]; the topological degree theory [7,11]; and so on [12]. It should be noted that compared to boundary-value problems for ordinary differential equations, there exist very less of multiplicity results for corresponding impulsive equations [1,10].…”