Can you spot the use of the derivative (calculus derivative) in this Paul Krugman post?
Delusion #2 is the belief that the stimulus may yet do the trick, because there are still substantial funds unspent. I tried to deal with this last year. The level of GDP depends not on total funds spent, but on the rate at which funds are being spent, which has already peaked; GDP growth on the rate of change in the rate at which funds are being spent, which peaked last year. It’s all downhill from here.