A tribe of people are posing for a picture.
Nobody is posing.
If people are posing, then it isn't true that nobody is posing.
exists e1 x1 x2 x3.(for(e1,x3) & n_picture(x3) & Actor(e1,x1) & v_pose(e1) & of(x1,x2) & n_people(x2) & n_tribe(x1))
-exists e1 x1.(Actor(e1,x1) & v_pose(e1) & n_person(x1))