1. The problem statement, all variables and given/known data I have the following graph theory problem: 2. Relevant equations The only theorem I know about SDRs is Hall's theorem: Let S_1, ... , S_k be finite sets. S_1, ... , S_k has an SDR if and only if the union of any n of the sets has at least n elements. 3. The attempt at a solution I have no idea how to start. The only theorem we've gone over in class dealing with SDRs is Hall's, but I have no idea how to apply that.