A group of girls sit back to back.
Girls are jump roping.
One can not be jump roping 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 p1 x1.(exists x2 x3.((x1 = x2) & n_rope(x2) & of(x2,x3) & n_jump(x3)) & n_girl(x1))