Deficiency of a graph

Deficiency of a graph --- дефицит графа.

Let $M$ be a matching in a graph $G$. A vertex $v$ is saturated by $M$ if an edge of $M$ is incident with $v$, otherwise $v$ is said to be unsaturated.

The deficiency $def(G)$ of the graph $G$ is the number of vertices unsaturated by a maximum matching. Thus, if $def(G) = 0$, then $G$ has a perfect matching.