theorem
  Partial_Sums(- seq) = - Partial_Sums(seq)
proof
  Partial_Sums((-1r) * seq) = (-1r) * Partial_Sums(seq) by Th3;
  then Partial_Sums(- seq) = (-1r) * Partial_Sums(seq) by CSSPACE:70;
  hence thesis by CSSPACE:70;
end;
