theorem Th8:
  i divides j & i divides h implies i divides j+h
proof
  assume that
A1: i divides j and
A2: i divides h;
A3: j = i * (j div i) by A1,Th3;
  h = i * (h div i) by A2,Th3;
  then j + h = i * ((j div i) + (h div i)) by A3;
  hence thesis;
end;
