A boy mountain bikes down a trail.
A boy is riding a bike.
Mountain bikes down a trail implies riding a bike.
exists x1 x2 x3 x4.(a_topic(x1) & down(x1,x4) & n_trail(x4) & n_bike(x1) & of(x1,x3) & n_mountain(x3) & of(x1,x2) & n_boy(x2))
exists e1 x1 x2.(Theme(e1,x2) & Actor(e1,x1) & v_ride(e1) & n_bike(x2) & n_boy(x1))