A band performs on a stage.
A band plays a song.
A band may perform on stage without playing a song.
exists e1 x1 x2.(on(e1,x2) & n_stage(x2) & Actor(e1,x1) & v_perform(e1) & n_band(x1))
exists e1 x1 x2.(Theme(e1,x2) & Actor(e1,x1) & v_play(e1) & n_song(x2) & n_band(x1))