A girl is sleeping on the grass
A girl is not sleeping
A girl can't be sleeping and not sleeping at the same time
exists e1 x1 x2.(n_grass(x2) & on(e1,x2) & Actor(e1,x1) & v_sleep(e1) & n_girl(x1))
exists x1.(-exists e1.(Actor(e1,x1) & v_sleep(e1)) & n_girl(x1))