A policeman on a horse surrounded by onlookers.
the policeman is riding a horse.
For a policeman to be riding a horse, he must be on the horse.
exists e1 x1 x2 x3 x4.(a_topic(x1) & on(x1,x2) & Actor(e1,x4) & n_onlooker(x4) & Theme(e1,x3) & v_surround(e1) & (x2 = x3) & n_horse(x2) & n_policeman(x1))
exists e1 x1 x2.(n_policeman(x1) & Theme(e1,x2) & Actor(e1,x1) & v_ride(e1) & n_horse(x2))