Every intervention to prop up the yen is also creating a fresh opportunity to sell it.
The historic joint U.S.-Japan action last month has done little to shift the forces weighing on the currency, with the yen sliding back toward ?160 per dollar less than two weeks later.
The key is the wide gap between interest rates in Japan and elsewhere. Investors can borrow the low-yielding yen and use the money to buy higher-yielding assets ¡ª a strategy known as the carry trade.
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