Not a great coupling. Why?
A stable marriage is a marriage in which no boy-girl pair would want to swap spouses.
Such a pair is unstable because they'd rather dump their partners and marry each other than stay with who they've got.
Theorem 1: If there is no unstable pair, then there is also no unstable coalition. Why? A coalition is really just a set of pairs.
Can you find a stable marriage for this group?
