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Seymour Conjecture


For every positive integer k, the Seymour conjecture (Seymour 1974) asserts that a graph G of vertex count n>=3 with minimum vertex degree delta(G)>=kn/(k+1) contains the kth graph power of a Hamiltonian cycle, generalizing Pósa's conjecture. Komlós et al. (1998) proved the conjecture for sufficiently large n using Szemerédi's regularity lemma and a technique called the blow-up lemma.

A randomly augmented variant starts with a graph G of minimum vertex degree at least (2/3+epsilon)n, for a fixed epsilon>0, and adds an independent random graph G(n,p) on the same vertex set, with each pair of distinct vertices joined independently with probability p. For every epsilon>0, there is a constant c_1>0 such that p>=c_1n^(-2/5) guarantees that G union G(n,p) contains the 11th graph power of a Hamiltonian cycle with probability tending to 1 as n->infty. Conversely, for some epsilon>0 and c_0>0, there is a sequence of graphs meeting the same degree condition for which p<=c_0n^(-2/5) gives probability tending to zero. Thus n^(-2/5) is the threshold scale for this augmentation problem (Antoniuk et al. 2026, pp. 2, 6).


See also

Hajnal-Szemerédi Theorem, Hamiltonian Cycle, Pósa's Conjecture, Pósa's Theorem, Szemerédi's Regularity Lemma

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References

Antoniuk, S.; Dudek, A.; and Ruciński, A. "Powers of Hamiltonian Cycles in Randomly Augmented Pósa-Seymour Graphs." Elec. J. Combin. 33, P4.26, 2026. https://doi.org/10.37236/15044.Faudree, R. J.; Gould, R. J.; Jacobson, M. S.; and Schelp, R. H. "On a Problem of Paul Seymour." In Recent Advances in Graph Theory (Ed. V. R. Kulli). Vishwa International Publishers, pp. 197-215, 1991.Komlós, J.; Sárkőzy, G. N.; and Szemerédi, E. "On the Square of a Hamiltonian Cycle in Dense Graphs." In Random Structures Algorithms 9, 193-211, 1996.Komlós, J.; Sárkőzy, G. N.; and Szemerédi, E. "Proof of the Seymour Conjecture for Large Graphs." Ann. Comb. 2, 43-60, 1998.Seymour, P. Problem Section in Combinatorics: Proceedings of the British Combinatorial Conference, 1973 (Ed. T. P. McDonough and V. C. Mavron). Cambridge, England: Cambridge University Press, pp. 201-202, 1974.

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Seymour Conjecture

Cite this as:

Weisstein, Eric W. "Seymour Conjecture." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/SeymourConjecture.html

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