  (3) As the return on investment is positive \((\mu \gt 0)\), the arrow of time displays a bias in favour of future generations (Sect. 2.1). But the larger is the chosen value of \(\sigma\), the more DM displays concerns over equity in consumption across the generations. Therefore, the larger is that concern, the higher is the optimum rate of consumption to be enjoyed by initial generations. So we should expect the optimum rate of saving to be a decreasing function of \(\sigma\), other things equal.