A boy on a scooter.
A boy riding around.
On a scooter does not necessarily mean riding around.
exists x1 x2.(a_topic(x1) & on(x1,x2) & n_scooter(x2) & n_boy(x1))
exists e1 p1 x1 x2.(a_topic(x1) & exists s1.(Theme(s1,x2) & a_around(s1)) & Topic(e1,p1) & Actor(e1,x2) & v_ride(e1) & (x1 = x2) & n_boy(x1))