theorem
  seq is convergent & lim seq = g implies ||.(- seq) - (- g).|| is
  convergent & lim ||.(- seq) - (- g).|| = 0
proof
  assume seq is convergent & lim seq = g;
  then - seq is convergent & lim (- seq) = - g by Th6,Th16;
  hence thesis by Th22;
end;
