theorem
  seq1 is convergent & lim seq1 = g1 & seq2 is convergent & lim seq2 =
  g2 implies dist((seq1 - seq2) , (g1 - g2)) is convergent & lim dist((seq1 -
  seq2) , (g1 - g2)) = 0
proof
  assume seq1 is convergent & lim seq1 = g1 & seq2 is convergent & lim seq2 =
  g2;
  then seq1 - seq2 is convergent & lim (seq1 - seq2) = g1 - g2 by Th4,Th14;
  hence thesis by Th24;
end;
