a dog runs for the tennis ball.
A dog is running after a soccer ball.
A tennis ball and soccer ball are different balls
exists e1 x1 x2 x3.(n_ball(x2) & of(x2,x3) & n_tennis(x3) & for(e1,x2) & Actor(e1,x1) & v_run(e1) & n_dog(x1))
exists e1 x1 x2 x3.(after(e1,x2) & n_ball(x2) & of(x2,x3) & n_soccer(x3) & Actor(e1,x1) & v_run(e1) & n_dog(x1))