Dirac's theorem and Ore's theorem
Two sufficient (not necessary) degree conditions that guarantee a graph is Hamiltonian: Dirac's checks every vertex's own degree, Ore's checks the degree sum of every non-adjacent pair.
Dirac's theorem: if every vertex of a simple graph on n\ge3 vertices has degree \ge n/2, the graph is Hamiltonian (theorem: diracs-theorem). Ore's theorem: if \deg(u)+\deg(v)\ge n for every non-adjacent pair u,v, the graph is Hamiltonian (theorem: ores-theorem) -- Dirac's is a direct corollary.
See also
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