The girls are playing soccer.
Nobody is playing.
If there are nobody playing then there are are no girls playing.
exists e1 x1 x2.(n_girl(x1) & Theme(e1,x2) & Actor(e1,x1) & v_play(e1) & n_soccer(x2))
-exists e1 x1.(Actor(e1,x1) & v_play(e1) & n_person(x1))