A chemist, an engineer and an economist joke

A chemist, an engineer and an economist are stranded on a deserted island. They carry with them some canned food but have no ordinary means of opening the cans. The chemist suggests gathering some wood and starting a fire and then holding the cans over the heat, counting on the expanding contents to burst open the cans. The engineer thinks it would be better to try smashing the cans open with some of the rocks lying around. The economist begins, “Assume we had a can opener…”