Guys are running in a marathon.
The guys are all friends.
You can't tell if the guys running the marathon are all friends.
exists e1 x1 x2.(in(e1,x2) & n_marathon(x2) & Actor(e1,x1) & v_run(e1) & n_guy(x1))
exists p1 x1.(n_guy(x1) & all x2.(n_friend(x2) -> (x1 = x2)))