A singer performs on stage at a concert.
A person is singing
A person refers to singer, he is in stage so he is singing.
exists e1 x1 x2 x3.(at(e1,x3) & n_concert(x3) & on(e1,x2) & n_stage(x2) & Actor(e1,x1) & v_perform(e1) & n_singer(x1))
exists e1 x1.(Actor(e1,x1) & v_sing(e1) & n_person(x1))