A boy standing on railing
A boy is skating on a street.
Boy cannot be standing and skating at same time.
exists e1 e2 x1 x2 x3.(a_topic(x1) & on(e1,e2) & Actor(e2,x3) & v_rail(e2) & Actor(e1,x2) & v_stand(e1) & (x1 = x2) & n_boy(x1))
exists e1 x1 x2.(on(e1,x2) & n_street(x2) & Actor(e1,x1) & v_skate(e1) & n_boy(x1))