Function application is represented by
adjacent closed figures, and arrows point from the applied functions to their argument. In VEX, free and
bound identifiers are easily recognized. Each identifier is connected by an undirected edge to a labeled root
node. Free identifiers are connected to roots which are not inside and tangent to any rings, while bound
identifiers are connected to internally tangent roots. Thus, in Figure 12 identifier 2 is free in the overall
expression while identifier 5 is bound inside the expression represented by ring 3. Graphical equivalents have
been devised for -conversion, -reduction, and -reduction, but a detailed discussion of these is beyond the
scope of this report.