Participants are on horses competing in a game
People on horses are outside.
Participants are people.
exists p1 x1.(exists e1 x2 x3 x4.(on(x1,x2) & in(e1,x4) & n_game(x4) & Actor(e1,x3) & v_compete(e1) & (x2 = x3) & n_horse(x2)) & n_participant(x1))
exists s1 x1 x2.(Theme(s1,x1) & a_outside(s1) & on(x1,x2) & n_horse(x2) & n_people(x1))