theorem
  seq is convergent & lim seq = g implies dist((z * seq) , (z * g)) is
  convergent & lim dist((z * seq) , (z * g)) = 0
proof
  assume seq is convergent & lim seq = g;
  then z * seq is convergent & lim (z * seq) = z * g by Th5,Th15;
  hence thesis by Th24;
end;
