.IF THERE IS one iron rule of money management, it is actually that any kind of system which seems to produce huge, trusted revenues is hiding some likewise big dangers. Past history is stuffed along with instances of such money-spinners coming to be hugely preferred, just for enthusiasts to belatedly realise that they can generate sudden losses in addition to consistent increases. Should that compel bunches of people to abandon comparable fields simultaneously, the knock-on effects may endanger all kind of different resources, and even the economic body on its own. Think of the massive bets on subprime mortgage loans that preceded the global financial crisis of 2007-09. The latest example is the Eastern yen "lug exchange", the unwinding of which has been roiling markets considering that mid-July while quickly enhancing the market value of the yen. What is a hold exchange, as well as how can it untangle therefore strongly?