 As seen in the previous subsection, including relations (not just qualities) in algebraic expressions and representing the universal quantifier as products (i.e., \(\Pi\)) and the existential quantifier as sums (i.e., \(\Sigma\)) were the main output of Peirce’s two decade tireless work. Considering Schröder’s book was the most popular logic textbook for mathematical logic students during that era, we can easily say Peirce’s legacy has lived on. Peckhaus, working on a delicate relation between Frege’s and Schröder’s quantification theory, locates where Schröder’s modern quantification theory originates from: 