A girl sits on a swing.
A girls is playing at a park.
Many households with children have a swing at home, and swings are often at school playgrounds also. Neither are the park, and the girl could be at either instead.
exists e1 x1 x2.(on(e1,x2) & n_swing(x2) & Actor(e1,x1) & v_sit(e1) & n_girl(x1))
exists e1 x1 x2.(at(e1,x2) & n_park(x2) & Actor(e1,x1) & v_play(e1) & n_girl(x1))