Teenagers enjoy skateboarding in a pedestrian area.
A teen rides his skateboard down a half pipe.
Not all teenagers enjoying skateboarding in a pedestrian area rides his skateboard down a half pipe.
exists e1 p1 x1.(exists e2 s1 x2.(in(e2,x2) & n_area(x2) & a_pedestrian(s1) & Theme(s1,x2) & Actor(e2,x1) & v_skateboard(e2)) & Topic(e1,p1) & Actor(e1,x1) & v_enjoy(e1) & n_teenager(x1))
(-x)