A performer on a concert stage.
The person is singing.
Not all concert stage performer are singing
exists x1 x2 x3.(a_topic(x1) & on(x1,x2) & n_stage(x2) & of(x2,x3) & n_concert(x3) & n_performer(x1))
exists e1 x1.(n_person(x1) & Actor(e1,x1) & v_sing(e1))