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On Essential and Inessential Polygons in Embedded Graphs
AbstractIn this article, we present a number of results of the following type: A given subgraph of an embedded graph either is embedded in a disc or it has a face chain containing a non-contractible closed path. Our main application is to prove that any two faces of a 4-representative embedding are simultaneously contained in a disc bounded by a polygon. This result is used to prove the existence of β(rβ1)/8β pairwise disjoint, pairwise homotopic non-contractible separating polygons in an r -representative orientable embedding. Our proof of this latter result is simple and mechanical