Simple drawing

The nodes are laid out as dots on a sheet of paper, frequently labelled by the members of the set N. The links are represented by arrows joining the nodes, the arrow runs from node i to node j if . Note that there is no requirement that both and belong to L, nor that either belongs or does not belong.

It is a classical problem in graph theory, to decide whether a graph may be drawn in two dimensions so that its links do not cross; this point does not interest us except insofar as the aesthetics of laying out the graph is concerned.

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Harold V. McIntosh
E-mail:mcintosh@servidor.unam.mx