theorem Th3:
  |.i.| <= 2 implies i = -2 or i = -1 or i = 0 or i = 1 or i = 2
  proof
    assume |.i.| <= 2;
    then |.i.| = 0 or ... or |.i.| = 2;
    hence thesis by ABSVALUE:2,Th2;
  end;
