A girl is playing on a swing.
A girl is on the swing.
girl is on the swing implies she is playing.
exists e1 x1 x2.(on(e1,x2) & n_swing(x2) & Actor(e1,x1) & v_play(e1) & n_girl(x1))
exists p1 x1 x2.(n_swing(x2) & on(x1,x2) & n_girl(x1))