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Given that $Q_d$ is the hypercube graph of dimension $d$ then it is a known fact (not so trivial to prove though) that given a perfect matching $M$ of $Q_d$ ($d\geq 2$) it is possible to find another perfect matching $N$ of $Q_d$ such that $M \cup N$ is a Hamiltonian cycle in $Q_d$.

The question now is - given a (non necessarily perfect) matching $M$ of $Q_d$ ($d\geq 2$) is it possible to find a set of edges $N$ such that $M \cup N$ is a Hamiltonian cycle in $Q_d$.

The statement is proven to be true for $d \in\{2,3,4\}$.

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up vote 14 down vote accepted

This is a known open problem. See "Matchings extend to Hamiltonian cycles in hypercubes" over at the Open Problem Garden.

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