13A brief terminological rant: We generally call b ‘wealth’ rather than ‘savings’ because of the confusion induced by the words ‘saving’ and ‘savings’; saving is a behavior (a flow; a choice not to spend some portion of current income) while savings is a stock of resources that result from past saving flows. Authors in this literature frequently misapply the stock word savings for the flow word saving or vice versa, so we prefer to use the word ‘wealth’ which unambiguously denotes a stock.