Blocking pair in stable matching
= Blocking pair in stable matching
{title2=$r\succ_\ell M(\ell),\ \ell\succ_r M(r)$}
An acceptable unused <edge> whose endpoints both prefer each other to their partners in a <matching in a graph>, treating every acceptable partner as preferable to being unmatched. A <stable matching> has no such <edge>. In the worked example, $(B,Y)$ blocks $N$ even though $A$ already has its first choice.