People in the city.
People at a music festival
A music festival is not necessarily held in the city.
exists x1 x2.(n_city(x2) & a_topic(x1) & in(x1,x2) & n_people(x1))
exists x1 x2 x3.(a_topic(x1) & at(x1,x2) & n_festival(x2) & of(x2,x3) & n_music(x3) & n_people(x1))