  The discovery of Leibniz in mathematical logic can be shown by example in the case of George Boole, the founder of the algebra of logic (cf. Peckhaus 1997, 185–232; on Ernst Schröder’s discovery of Leibniz cf. ibid., 233–287). In his first writing on logic, the booklet The Mathematical Analysis of Logic of 1847, he gave an algebraic interpretation of traditional logic. His fame as one of the founders of modern logic goes back to his An Investigation of the Laws of Thought of 1854. According to Boole’s own evaluation, his main innovation was the Index Law (1847), later revised to the Law of Duality, also called “Boole’s Law”. This law expresses idempotence: