Graphical scenes are represented as values of type Picture, a recursive data type that contains both the geometric primitives supported, and the core set of operators that transform and combine Pictures together. Rather than go through the whole {\tt Picture} (Appendix See section Complete picture type has the complete definition), type from top to bottom, let's instead focus on a simple example of a picture and the issues and features that highlight for the Picture type. The picture is that of a traffic light (shown here horizontally to save space):
\vspace{0.15in} \centerline{\psfig{figure=tlight.eps}}