A group of girls sit back to back.
The girls are skipping rope.
One can not be skipping rope and sit simultaneously.
exists e1 s1 x1 x2 x3.(Theme(e1,s1) & Theme(s1,x3) & a_back(s1) & r_back(e1) & Actor(e1,x1) & v_sit(e1) & of(x1,x2) & n_girl(x2) & n_group(x1))
exists e1 x1 x2.(n_girl(x1) & Theme(e1,x2) & Actor(e1,x1) & v_skip(e1) & n_rope(x2))