The first phase of the coronavirus outbreak was a domestic challenge for China and a border containment one for the United States and others. Now we are in the second phase: community mitigation. Math and history must guide our next steps. The near-term objective should be to reduce the acute, exponential growth of the outbreak, in order to reduce suffering and the strain on our health-care system. That will require significant effort, but it can work, as we have seen: Hong Kong and Singapore have achieved linear growth of covid-19 cases, staving off the terrifying exponential upward curve confronting Italy...