Tantrums are habit-forming, or so you argue about the market’s refusal to be appeased by sundry toys thrown into its baby carriage by ever more frantic governments (“Carry on Screaming,” October 11, 2008).  “You might have thought that interest-rate cuts were the answer,” you go on, “until you saw the market response to the coordinated announcements from the Federal Reserve and others on October 8.”  Anyone who still remembers Keynes’ “liquidity trap” from the first course in macroeconomics would not be fooled so easily, though.  The closer the nominal interest rate to zero, the less effective its reduction in downturns.  In the limit, it becomes irrelevant.  Whence the awkward trap.  Sadly, Ben Bernanke must have been asleep at that particular lecture, as he drove the rate all the way down in one fell swoop at the very onset of the crisis in January.