a skateboarder grinds the rail.
A tall skateboarder
Not all skateboarders are tall.
exists e1 x1 x2.(n_rail(x2) & Theme(e1,x2) & Actor(e1,x1) & v_grind(e1) & n_skateboarder(x1))
exists s1 x1.(a_topic(x1) & n_skateboarder(x1) & a_tall(s1) & Theme(s1,x1))