Abstract
For a given graph property \(\mathcal {P}\), we say a graph G is locally \(\mathcal {P}\) if for each \(v \in V(G)\), the subgraph induced by the open neighbourhood of v has property \(\mathcal P\). A closed locally \(\mathcal {P}\) graph is defined analogously in terms of closed neighbourhoods. It is known that connected locally hamiltonian graphs are not necessarily hamiltonian. Saito (in Computational Geometry and Graph Theory, Lecture Notes in Computer Science, vol. 4535, pp. 191–200. Springer, Berlin, 2008) conjectured that if G is a graph of order at least 3 such that for every vertex v in G the subgraph induced by the closed neighbourhood N[v] of v satisfies the Chvátal–Erdős condition for hamiltonicity, then G is hamiltonian. Oberly and Sumner (in J Graph Theory 3:351–356, 1979) conjectured that if G is a connected, locally k-connected \(K_{1,k+2}\)-free graph of order at at least 3, then G is hamiltonian. We prove a result that lends support to both these conjectures. We also provide a framework for investigating these and other related conjectures.
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Acknowledgements
The authors wish to express gratitude to the Banff International Research Station for their support of the focused research workshop “Local Properties in Graphs that imply Global Cycle Properties” (15frg184), where this paper originated.
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S. A. van Aardt: Supported by the National Research Foundation of S.A., Grant Number 81075, M. Frick: Supported by the National Research Foundation of S.A., Grant Number 81004, O. R. Oellermann: Supported by an NSERC Grant CANADA, Grant Number RGPIN-2016-05237.
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van Aardt, S.A., Dunbar, J.E., Frick, M. et al. On Saito’s Conjecture and the Oberly–Sumner Conjectures. Graphs and Combinatorics 33, 583–594 (2017). https://doi.org/10.1007/s00373-017-1820-5
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DOI: https://doi.org/10.1007/s00373-017-1820-5
Keywords
- Saito’s conjecture
- Oberly–Sumner conjectures
- Hamiltonian
- Fully cycle extendable
- Locally k-connected
- \(K_{1 , k}\)-free
- Locally k-\(P_3\)-connected