= Facial boundary walk
For a finite <connected graph> embedded as a <plane graph>, follow the <edges> around a <face of a plane graph> to obtain a <closed walk>. Count traversals, not distinct <edges>: a <bridge in a graph> occurs twice along one <facial boundary walk>. Each <edge> contributes two sides in total.<Mathematics for Computer Science by Eric Lehman and others>[Mathematics for Computer Science, §12.4, Lemma 12.4.1, printed p. 485]{ref}
For the three-<vertex> <graph path> $A-B-C$, the only <facial boundary walk> is $A,B,C,B,A$, of length four. Both <edges> are <bridges in a graph>; neither is a <graph cycle>. Thus a <facial boundary walk> need not be a <graph cycle>.
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