Ugh, splitting the bill. At worst it’s like showing your parents around the touristy bits of town — expensive, unfun, leaving everyone involved with the feeling that they’ve been shafted. Inevitably someone skips the starter; someone else orders two sides; somebody's off the sauce; puddings either divide opinion or are themselves divided by two or more diners. Simple game theory points to one way to sort this out. Before the meal, everyone should agree......