 In the 1690s, Johann Bernoulli, who was rated by Johann Bernoulli as one of the five greatest mathematicians in Europe, began teaching calculus to Guillaume de L'Opital, a French nobleman whose nearsightedness disqualified him for military service. L'Opital proved to be a good student, and decided to write a textbook on calculus, the first ever written. He hired his old teacher as a consultant. In exchange for a rather considerable sum of money, Bernoulli agreed to answer questions presented by L'Opital, and, in modern terms, waived rights to his intellectual property. In the course of writing his book, L'Opital came across a type of problem that had never been solved before, and asked Bernoulli about it. Bernoulli solved the problem, L'Opital published it in his book, and the method has ever since been known as L'Opital's Rule. And while it was, in fact, discovered by Johann Bernoulli, it is, in fact, L'Opital's Rule, bought and paid for.