Try to use the principle of lever to explain why the moving pulley is labor-saving

Try to use the principle of lever to explain why the moving pulley is labor-saving

The movable pulley is twice the power arm and the resistance arm, L1 = 2l2
According to the formula f1l1 = f2l2: F1 = f2l2 / L1 = F2 / 2
So moving the pulley can save half the force