A simple model of "hourglass" problems is presented. For such problems, the benefit of a national policy measure is propagated to all countries through one single world-wide variable. The prime example is the effect of the reduction of CO2 emission on the world climate.Five optimal solutions are...

This paper discusses a widely used discrete-time analog of dynamic continuous-time models. This analog can not be used for the estimation of models with fast adaption to shocks. This has been overlooked in the econometric literature. In the engineering literature this same analogon is defined,...