theorem Th28:
  1 <= Sum(||.z.|| rExpSeq)
proof
  ||. Partial_Sums(z ExpSeq).0 .|| =||. (z ExpSeq).0 .|| by BHSP_4:def 1
    .=||. 1.X.|| by Th13
    .=1 by CLOPBAN3:38;
  hence thesis by Th27;
end;
