theorem Th16:
  Sum(seq,1) = Sum(seq,0) + seq.1
proof
  Partial_Sums(seq).1 = Partial_Sums(seq).0 + seq.(0 + 1) by BHSP_4:def 1
    .= Partial_Sums(seq).0 + seq.1;
  hence thesis;
end;
