==> probability/darts.p <==
Peter throws two darts at a dartboard, aiming for the center.  The
second dart lands farther from the center than the first.  If Peter now
throws another dart at the board, aiming for the center, what is the
probability that this third throw is also worse (i.e., farther from 
the center) than his first?  Assume Peter's skilfulness is constant.