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DM
2008
15 years 9 days 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...
90
Voted
DM
2008
15 years 25 days 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,...
95
Voted
DM
2008
15 years 25 days 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 ...
71
Voted
DM
2008
15 years 25 days 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...
98
Voted
DM
2008
15 years 25 days 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...