A performer on a concert stage.
The person is on stage.
As they are both on a stage, the person must also be the performer.
exists x1 x2 x3.(a_topic(x1) & on(x1,x2) & n_stage(x2) & of(x2,x3) & n_concert(x3) & n_performer(x1))
exists p1 x1.(n_person(x1) & exists x2.(on(x1,x2) & n_stage(x2)))