For some time now, the smart take on China’s currency has been that the Chinese authorities have been intervening — but to prop up the yuan not to hold it down. In other words, perennial U.S. complaints about China artificially manipulating its currency to gain a trade advantage were out of date. That claim itself is now, well, dated. And clearly wrong. The preponderance of evidence now shows that China is once again intervening to hold its currency down. It is doing so to gain a trade