A man is grinding his skateboard on a guard rail.
The man is a professional skateboarder.
Not all skateboarders are professional.
exists e1 x1 x2 x3 x4.(Theme(e1,x2) & Actor(e1,x1) & v_grind(e1) & on(x2,x3) & n_rail(x3) & of(x3,x4) & n_guard(x4) & n_skateboard(x2) & of(x2,x1) & n_male(x1) & n_man(x1))
exists p1 x1.(n_man(x1) & exists s1 x2.((x1 = x2) & n_skateboarder(x2) & a_professional(s1) & Theme(s1,x2)))