uniform independent bits:X1,X2,...,XmE 10,1} nonempty subsets:S1,$2,...,S2m-1 {1,2,...,m} Y=①X iESj 2-wise independent uniform bits: Y1,Y2,.,Y2m-1∈{0,1 log2 n total random bits n-1 pairwise independent bitsX1, X2,...,Xm 2 {0, 1} nonempty subsets: S1, S2,...,S2m￾1 ✓ {1, 2,...,m} uniform & independent bits: Yj = M i2Sj Xi Y1, Y2,...,Y2m￾1 2 {0, 1} 2-wise independent uniform bits: log2 n total random bits n-1 pairwise independent bits