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132
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DM
2008
15 years 4 months ago
2008
Using results by McKee and Woodall on binary matroids, we prove that the set of postman sets has odd cardinality, generalizing a result by Toida on the cardinality of cycles in Eu...
118
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DM
2008
15 years 4 months ago
2008
We find the largest for which any simple closed path in the universal cover R2 \ Z2 of R2 \ Z2, equipped with the natural lifted metric from the Euclidean two dimensional plane,...
127
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DM
2008
15 years 4 months ago
2008
A vertex v of a graph G is a boundary vertex if there exists a vertex u such that the distance in G from u to v is at least the distance from u to any neighbour of v. We give the ...
106
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DM
2008
15 years 4 months ago
2008
The poset retraction problem for a poset P is whether a given poset Q containing P as a subposet admits a retraction onto P, that is, whether there is a homomorphism from Q onto P...
127
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DM
2008
15 years 4 months ago
2008
In [2], Duffus et al. showed that every connected graph G which contains no induced subgraph isomorphic to a claw or a net is traceable. And they also showed that if a 2-connected...