reserve r for Real;

theorem Th29:
  for x,y,z being Element of 2 holds
  Set_to_zero.(x,z) <= Set_to_zero.(x,y) + Set_to_zero.(y,z)
proof
  let x,y,z be Element of 2;
  Set_to_zero.(x,y) = 0 & Set_to_zero.(y,z) = 0 by Th27;
  hence thesis by Th27;
end;
