Photographers taking pictures of each other.
The people are at a photo shoot.
People at a photo shoot aren't always photographers, and aren't necessarily taking pictures of each other.
exists x1 x2 x3.(a_topic(x1) & all x4.(n_other(x4) -> exists e1.(Theme(e1,x3) & Actor(e1,x2) & v_take(e1) & of(x3,x4))) & n_picture(x3) & (x1 = x2) & n_photographer(x1))
exists p1 x1.(n_people(x1) & exists x2 x3.(at(x1,x2) & n_shoot(x2) & of(x2,x3) & n_photo(x3)))