The author is a Reuters Breakingviews columnist. The opinions expressed are his own.
Currency concerns in the central banking world have come to the fore again.
Sweden cut interest rates further into negative territory out of the blue last week, fearing its strong currency will engender deflation. The Swiss National Bank said it would aim to weaken what it sees as a "significantly overvalued" franc. And the Bank of England flagged the risk that sterling could strengthen further and leave inflation below target for longer.