Codified discounting solves pricing problems including markups and markdowns. In the UK, the main difference between factoring and invoice discounting is confidentiality. Economic theory suggests that optimal discounting involves the exponential discounting of value over time. The discounting of monetary rewards varies across age groups due to the varying discount rate. Exponential discounting is not dynamically inconsistent. However, alternatives like hyperbolic discounting have more empirical support. This evidence only supports hyperbolic discounting, not exponential. Exponential discounting yields time-consistent preferences. In other words, prices are the result of discounting expected future cash flows. The findings led to the model of exponential discounting, thus time consistent discounting. Several alternative explanations of non-exponential discounting have been proposed. Hotels are still prevented from discounting prices directly on their own websites. Turner ensured that the license agreements forbade retailers from discounting "Quest" items. The disagreement has sparked a vigorous debate on issue of discounting and intergenerational equity. This effect is called hyperbolic discounting.