编写要求：
MACD零轴下首次死叉选股公式.
公式在线网解答：
CROSS("MACD.DEA","MACD.DIF") AND "MACD.DEA"<0 AND COUNT(CROSS("MACD.DEA","MACD.DIF") AND "MACD.DEA"<0,BARSLAST(CROSS(0,"MACD.DEA")))=1;
