A person on a bmx bike.
A person is doing stunts.
Being on a bmx doesn't imply doing stunts.
exists x1 x2 x3.(a_topic(x1) & on(x1,x2) & n_bike(x2) & of(x2,x3) & n_bmx(x3) & n_person(x1))
exists e1 x1 x2.(Theme(e1,x2) & Actor(e1,x1) & v_do(e1) & n_stunt(x2) & n_person(x1))