Kenneth Rogoff, whose research into historical financial crises with Carmen Reinhart may be the most extensive ever performed, says the U.S. economy is following a normal post-financial-crisis path, but that troubles in the rest of the world are reason for worry. On Bloomberg Surveillance, Rogoff also says he thinks Greece will eventually leave the eurozone, and he talks about the importance of examining all forms of debt that impact the economy, not just those that are officially reported as government debt, when assessing economic health. And he discusses the issue of stimulus vs. austerity, and when he thinks stimulus is appropriate.