Consider the random walk Sn = So+Xi+...+ Xn, where X1, X2, ... are iid integer-valued random variables with EX; > 0, P[X; 2 -1] = 1, and P [Xi = -1] > 0. Let o(0) = Elexp(0X1)] be the moment generating function and let Va = min{n 2 0 : Sn = a} be the first visit time to a e Z.(i) Show that there exists a unique a