Girls are dancing and singing on stage.
The girls are seated in class.
The girls can not be dancing and singing while sitting down
exists e1 e2 x1 x2 x3 x4.(on(e2,x4) & n_stage(x4) & Actor(e2,x3) & v_sing(e2) & n_girl(x3) & on(e1,x2) & n_stage(x2) & Actor(e1,x1) & v_dance(e1) & n_girl(x1))
exists e1 x1 x2.(n_girl(x1) & in(e1,x2) & n_class(x2) & Theme(e1,x1) & v_seat(e1))