The VIPR group has also developed a visual representation for the lambda calculus which they refer to
as VEX for Visual EXpressions. VEX is intended to become an expression-oriented component of VIPR
[Citrin et al. 1995]. We will only take a brief look at its major features. Figure 11 shows the textual and
visual representations for the Y combinator. As in VIPR, parameters are represented by small circles inside
and tangent to main rings, so f and x are parameters in the example. 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.