Have you heard the joke about the chemist, physicist and economist who get wrecked on a desert isle, with a huge supply of canned baked beans as their only food? The chemist says that he can start a fire using the neighbouring palm trees, and calculate the temperature at which a can will explode. The physicist says that she can work out the trajectory of each of the baked beans, so that they can be collected and eaten. The economist says "Hang on guys, you're doing it the hard way. Let's assume we have a can opener.