System of Distinct Representatives (Transversal) system of distinct representatives(SDR) for sets S1,S2,...,Sm distinct x1,c2,·,xm xi∈Si for i=1,2,...mSystem of Distinct Representatives system of distinct representatives (SDR) for sets S1, S2,...,Sm distinct x1, x2,...,xm xi ￾ Si for i =1, 2, ..., m (Transversal)