"book-pflow-xyz/chapters/appendix-d-glossary.md" . . . "A read arc (fires only if a place holds a token, without consuming it) or an inhibitor arc (fires only if it holds none). Neither appears in the incidence matrix, since neither changes the marking. Nets with contextual arcs do not generate the free symmetric monoidal category of ordinary nets (Montanari & Rossi, 1995); they are the categorical half of the core–observer boundary, and the natural home of guards."@en . . "Contextual arc"@en .