A band is performing on stage.
A band is sleeping.
performing and sleeping can not happening at the same time
exists e1 x1 x2.(on(e1,x2) & n_stage(x2) & Actor(e1,x1) & v_perform(e1) & n_band(x1))
exists e1 x1.(Actor(e1,x1) & v_sleep(e1) & n_band(x1))