 Following De Morgan’s paper, Peirce, in his paper “Description of a Notation for the Logic of Relatives, resulting from an Amplification of the Conceptions of Boole’s Calculus of Logic” from 1870, lifted Boole’s work to the setting of binary relations—with binary relations one had, in addition to union, intersection and complement, the natural operations of composition and converse. A binary relation was characterized as a set of ordered pairs (see 3.328). He worked on this new calculus between 1870 and 1883. Like De Morgan, Peirce also considered a number of other natural operations on relations. Peirce’s main paper on the subject was “On the Algebra of Logic” (1880). By employing unrestricted unions, denoted by Σ, and unrestricted intersections, denoted by Π, Peirce thus introduced quantifiers into his algebra of logic.