A sheriff on a motorcycle leads a parade.
A normal person on a motorcycle
A sheriff is riding the motorcycle, not just a normal person.
exists e1 x1 x2 x3.(Theme(e1,x3) & Actor(e1,x1) & v_lead(e1) & n_parade(x3) & on(x1,x2) & n_motorcycle(x2) & n_sheriff(x1))
exists s1 x1 x2.(a_topic(x1) & on(x1,x2) & n_motorcycle(x2) & n_person(x1) & a_normal(s1) & Theme(s1,x1))