We show that in multi-sector optimal growth models, where the technology satisfies a simple reachability condition, infinite horizon programs which satisfy the competitive conditions are optimal. We provide examples of a variety of production models where the reachability condition is satisfied....

We consider dynamic competition among platforms in a market with network externalities. A platform that dominated the market in the previous period becomes “focal” in the current period, in that agents play the equilibrium in which they adopt the focal platform whenever such equilibrium...