A man riding a dirt bike
A man is on a dirt bike.
If a man is riding a dirt bike he must be on a dirt bike.
exists e1 x1 x2 x3 x4.(a_topic(x1) & Theme(e1,x3) & Actor(e1,x2) & v_ride(e1) & n_bike(x3) & of(x3,x4) & n_dirt(x4) & (x1 = x2) & n_man(x1))
exists p1 x1.(exists x2 x3.(on(x1,x2) & n_bike(x2) & of(x2,x3) & n_dirt(x3)) & n_man(x1))