a man participates in a bmx race.
A man is in a bike race.
bmx is a form o bike
exists e1 x1 x2 x3.(in(e1,x2) & n_race(x2) & of(x2,x3) & n_bmx(x3) & Actor(e1,x1) & v_participate(e1) & n_man(x1))
exists p1 x1.(exists x2 x3.(in(x1,x2) & n_race(x2) & of(x2,x3) & n_bike(x3)) & n_man(x1))