the usual one at 5 = 0 and a new one at 5 = A in which the initial state of the random walk 0 < 5(0) = i < A. Since the stopping time is the first time that S(n) = A then we can think of the spatial domain of the random walk as having two absorbing boundaries: the usual one at 5 = 0 and a new one at 5 = A