Spider diagrams of order

Abstract

Spider diagrams are a visual logic capable of making statements about relationships between sets and their cardinalities. Various meta-level results for spider diagrams have been established, including their soundness, completeness and expressiveness. Recent work has established various relationships between spider diagrams and regular languages, which highlighted various classes of languages that spider diagrams could not define. In particular, this work illustrated the inability of spider diagrams to place an order on certain letters in words. To overcome this limitation, in this paper we introduce spider diagrams of order, incorporating an order relation and present a formalisation of the syntax and semantics. Subsequently, we define the language of such a diagram and establish that the class of such languages includes that of the piecewise testable languages.