 All agent types belong to a set formula_4 called "signature".An interaction net that consists solely of edges is called a "wiring" and usually denoted as formula_5.A "tree" formula_6 with its "root" formula_7 is inductively defined either as an edge formula_7, or as an agent formula_1 with its free principal port formula_7 and its auxiliary ports formula_11 connected to the roots of other trees formula_12.