  We study the maximum cardinality matching problem in a standard distributed
setting, where the nodes $V$ of a given $n$-node network graph $G=(V,E)$
communicate over the edges $E$ in synchronous rounds. More specifically, we
consider the distributed CONGEST model, where in each round, each node of $G$
can send an $O(\log n)$-bit message to each of its neighbors. We show that for
every graph $G$ and a matching $M$ of $G$, there is a randomized CONGEST
algorithm to verify $M$ being a maximum matching of $G$ in time $O(|M|)$ and
disprove it in time $O(D + \ell)$, where $D$ is the diameter of $G$ and $\ell$
is the length of a shortest augmenting path. We hope that our algorithm
constitutes a significant step towards developing a CONGEST algorithm to
compute a maximum matching in time $\tilde{O}(s^*)$, where $s^*$ is the size of
a maximum matching.
