1. Span(graph): a categorical algebra of transition systems;Katis,1997
2. Tangled circuits;Rosebrugh,2012
3. P. Katis, N. Sabadini, R. Walters, 1997, Representing p/t nets in span(graph).
4. A formalization of the IWIM model;Katis,2000
5. A survey of graphical languages for monoidal categories;Selinger,2011