Consider an economy of two-period-lived people in overlapping generations. Each person produces from labour y goods when young but nothing when old. The number of people born doubles every period. There is the following capital technology: if kt goods per young person are turned into capital at time t, the capital produces f(kt) goods at t + 1. The diminishing marginal product of capital is f(kt). After production takes place, d units of capital are lost to depreciation. However, the remaining units