A man is skateboarding in front of a group of people.
A man on a skateboard.
For a man to be skateboarding, he must be on a skateboard.
exists e1 x1 x2 x3 x4.(in(e1,x2) & of(x2,x3) & of(x3,x4) & n_people(x4) & n_group(x3) & n_front(x2) & Actor(e1,x1) & v_skateboard(e1) & n_man(x1))
exists x1 x2.(a_topic(x1) & on(x1,x2) & n_skateboard(x2) & n_man(x1))