In this construction, we let {Xi} be a family of IID Bernoulli random variables with x = 1 and y = −1 in (7.3). Denoting the associated random walk by {Wt}, show that the binomial model (7.24) can be expressed as S(t) = u(t+Wt)/2d(t−Wt)/2S, t = 0, 1, 2, . . . , T.