a man on a horse, jumping over a horse hurdle.
A man is riding a horse in a race.
A man on a horse is not necessarily riding a horse in a race.
exists e1 x1 x2 x3 x4 x5.(a_topic(x1) & over(e1,x4) & n_hurdle(x4) & of(x4,x5) & n_horse(x5) & Actor(e1,x3) & v_jump(e1) & (x1 = x3) & on(x1,x2) & n_horse(x2) & n_man(x1))
exists e1 x1 x2 x3.(in(e1,x3) & n_race(x3) & Theme(e1,x2) & Actor(e1,x1) & v_ride(e1) & n_horse(x2) & n_man(x1))