theorem
  Partial_Sums(- seq) = - Partial_Sums(seq)
proof
  Partial_Sums((-1) * seq) = (-1) * Partial_Sums(seq) by Th3;
  then Partial_Sums(- seq) = (-1) * Partial_Sums(seq) by BHSP_1:55;
  hence thesis by BHSP_1:55;
end;
