A boy swings on a swing set.
A boy is playing.
When one swings, they can be considered to be playing.
exists x1 x2 x3 x4.(a_topic(x1) & on(x1,x3) & n_set(x3) & of(x3,x4) & n_swing(x4) & n_swing(x1) & of(x1,x2) & n_boy(x2))
exists e1 x1.(Actor(e1,x1) & v_play(e1) & n_boy(x1))