A group of girls sit back to back.
A group of girls sit with their backs to each other during school.
The girls could be sitting at any time, not just during school
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 x3.(all x4.(n_other(x4) -> exists x5.(during(e1,x5) & n_school(x5) & to(e1,x4))) & with(e1,x3) & n_back(x3) & of(x3,x1) & n_thing(x1) & Actor(e1,x1) & v_sit(e1) & of(x1,x2) & n_girl(x2) & n_group(x1))