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تسجيل مستخدم جديدResilient degree sequences with respect to Hamilton cycles and matchings in random graphs
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Posas theorem states that any graph $G$ whose degree sequence $d_1 le ldots le d_n$ satisfies $d_i ge i+1$ for all $i < n/2$ has a Hamilton cycle. This degree condition is best possible. We show that a similar result holds for suitable subgraphs $G$ of random graphs, i.e. we prove a `resilience version of Posas theorem: if $pn ge C log n$ and the $i$-th vertex degree (ordered increasingly) of $G subseteq G_{n,p}$ is at least $(i+o(n))p$ for all $i<n/2$, then $G$ has a Hamilton cycle. This is essentially best possible and strengthens a resilience version of Diracs theorem obtained by Lee and Sudakov. Chvatals theorem generalises Posas theorem and characterises all degree sequences which ensure the existence of a Hamilton cycle. We show that a natural guess for a resilience version of Chvatals theorem fails to be true. We formulate a conjecture which would repair this guess, and show that the corresponding degree conditions ensure the existence of a perfect matching in any subgraph of $G_{n,p}$ which satisfies these conditions. This provides an asymptotic characterisation of all degree sequences which resiliently guarantee the existence of a perfect matching.
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