Apex graph

In graph theory, a branch of mathematics, an apex graph is a graph that can be made planar by the removal of a single vertex. The deleted vertex is called an apex of the graph. We say an apex, not the apex because an apex graph may have more than one apex (for example, in the minimal nonplanar graphs K5 or K3,3, every vertex is an apex). The apex ...
Found on http://en.wikipedia.org/wiki/Apex_graph
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