IN JUST a few brutal months, the prospects for the world economy have deteriorated with remarkable speed. Rich countries had seemed set for a shallow, muddle-through recession; now a much deeper slump is on the cards. In a sign of growing concern about American consumers, the Treasury and Federal Reserve on November 12th focused their rescue efforts on loans for cars and college and on credit cards. Central banks, recently so fearful of inflation, are now slashing interest rates to stop it falling too far. It will not be easy: deflation