They are here to ensure no one crosses the barriers.
People are waving others through an opening
You can't ensure no one crosses if people are going through an opening.
exists p1 s1 x1 x4.(n_barrier(x4) & n_thing(x1) & Topic(s1,p1) & Actor(s1,x1) & a_here(s1) & -exists e2 e1 x2 x3.(Theme(e2,x2) & Actor(e2,x1) & v_ensure(e2) & Theme(e1,x4) & Actor(e1,x3) & v_cross(e1) & (x2 = x3) & n_one(x2)))
exists e1 x1 x2 x3.(through(e1,x3) & n_opening(x3) & Theme(e1,x2) & Actor(e1,x1) & v_wave(e1) & -(x2 = x1) & n_person(x1) & n_person(x2) & n_people(x1))