Mario Draghi, himself an economist of some renown, this week unveiled a report on how to revive Europe’s flagging economic prospects. His answer: “Assume €800bn” (close to $900bn). That is the annual investment the former boss of the bloc’s central bank thinks is required to prevent the European Union’s economy falling ever further behind America’s. The problem is that money on that scale is as elusive in Europe as a tin-opener on a desert island. Establishing blueprints for spending money is the easy bit. But given EU countries are trillions of euros in debt beyond what the club’s own rules are meant to allow, finding the cash is likely to prove as hard as coming up with a funny joke involving economists.