Let G be a quadrangulation on a surface, and let f be a face bounded by a 4-cycle abcd. A face-contraction of f is to identify a and c (or b and d) to eliminate f . We say that a simple quadrangulation G on the surface is k-minimal if the length of a shortest essential cycle is k(โฅ 3), but any face-
Minimal embeddings in the projective plane
โ Scribed by Randby, Scott P.
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 161 KB
- Volume
- 25
- Category
- Article
- ISSN
- 0364-9024
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โฆ Synopsis
We show that if G is a graph embedded on the projective plane in such a way that each noncontractible cycle intersects G at least n times and the embedding is minimal with respect to this property (i.e., the representativity of the embedding is n), then G can be reduced by a series of reduction operations to an n ร n ร n projective grid. The reduction operations consist of changing a triangle of G to a triad, changing a triad of G to a triangle, and several others. We also show that if every proper minor of the embedding has representativity < n (i.e., the embedding is minimal), then G can be obtained from an n ร n ร n projective grid by a series of the two reduction operations described above. Hence every minimal embedding has the same number of edges.
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