Hall's Theorem(marriage theorem) S1:S2;...,Sm have a SDR VI C{1,2,...,m},Uier Si.S1, S2,...,Sm have a SDR Hall’s Theorem (marriage theorem) ⇥I ￾ {1, 2,...,m}, ￾ ￾ ⇥ i￾I Si ￾ ￾ ￾ |I|