IN GORDIUM in the fourth century B.C., an oxcart was roped to a pole with a complex knot, and it was said that the first person to untie it would become the king of Asia. Unfortunately, the knot proved impossible to untie. Legend has it that when confronted with this problem, rather than deliberating on how to untie the knot, Alexander simply took his sword and cut it in two—then went on to conquer Asia. Ever since, the notion of a “Gordian solution” has referred to the attractiveness of a simple answer to an otherwise intractable problem.