 Interestingly enough, when Peirce considered a graphic system his first concern was representation of relations, not representation of quantifiers. As we said in §3.1, Peirce presented diagrammatic representation based on an analogy to chemical molecules for a full understanding of relations. Hence, the arity of a predicate is represented by the number of lines radiating from the predicate term. Next, Peirce extends the use of a line to connect predicates: