Former Federal Reserve boss Alan Greenspan yesterday labeled Medicare the largest looming problem facing the US and said it was "very dangerous" to the nation's economic health. Speaking at a gathering of real estate executives ......the venerable banker knocked oil estimates and declared the housing boom "over", hedge funds will go belly up and declared immigrants with Ph.D.s in science or math should automatically get green cards. He also said the biggest problems facing the U.S. were "political," advising that Medicare costs by 2025 would cause an "unstable equilibrium" of debt, interest rates and deficits........a "highly unstable situation" and a...