A skateboarder skating at a skate park.
The young man is doing tricks on a skateboard.
The skateboarder is skating but he isn't necessarily doing tricks.
exists e1 x1 x2 x3 x4.(a_topic(x1) & at(e1,x3) & n_park(x3) & of(x3,x4) & n_skate(x4) & Actor(e1,x2) & v_skate(e1) & (x1 = x2) & n_skateboarder(x1))
exists e1 s1 x1 x2 x3.(n_man(x1) & a_young(s1) & Theme(s1,x1) & on(e1,x3) & n_skateboard(x3) & Theme(e1,x2) & Actor(e1,x1) & v_do(e1) & n_trick(x2))