“I’ll build a stairway to Paradise,” promised songwriter George Gershwin decades ago. Fed chairwoman Janet Yellen is about to try to do the same, taking interest rates up that stairway, from the zero level set during the hellish days of the financial crisis to the Paradise of normality or near-normality. There is almost unanimous agreement – an 85 percent probability according to markets — that next week the Federal Reserve Board’s monetary policy committee will raise interest rates by 0.25 percent, bringing the era of zero interest rates to an end. Unless, of course, Yellen & Co. belie the hints its chair has been dropping and double-cross the markets.