Two girls sit back to back.
Two girls are posing for a picture.
Just because the two girls are sitting back to back, it does not mean they are posing for a picture.
exists e1 s1 x1 x2.(Theme(e1,s1) & Theme(s1,x2) & a_back(s1) & r_back(e1) & Actor(e1,x1) & v_sit(e1) & n_girl(x1) & card_eq_2(x1))
exists e1 x1 x2.(for(e1,x2) & n_picture(x2) & Actor(e1,x1) & v_pose(e1) & n_girl(x1) & card_eq_2(x1))