People are walking by a building.
They are in a city.
Not all buildings are in a city.
exists e1 x1 x2.(by(e1,x2) & n_building(x2) & Actor(e1,x1) & v_walk(e1) & n_people(x1))
exists p1 x1.(n_thing(x1) & exists x2.(in(x1,x2) & n_city(x2)))