Imagine that you are trying to predict the level of real per capita GDP in a certain

economy in the year 2070 (say, using real dollars of some base year). Imagine that you

know exactly what productivity, defined as real GDP divided by the number of employed

workers, will be in that economy in that year. What other indicator/number/size/rate

about the economy do you need to know in order to make a perfect prediction? Specify

the exact definition of that indicator/number/size/rate.