Definition:Incident (Graph Theory)/Planar Graph

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Let $G = \left({V, E}\right)$ be a planar graph:

Then a face of $G$ is incident to an edge $e$ of $G$ if $e$ is one of those which surrounds the face.

Similarly, a face of $G$ is incident to a vertex $v$ of $G$ if $v$ is at the end of one of those incident edges.

In the above graph, for example, the face $ABHC$ is incident to:

the edges $AB, BH, HC, CA$
the vertices $A, B, H, C$.