The guard is looking at the city past the wall.
The policeman is looking over the neighborhood.
The guard may or may not be a policeman. Looking at the city is a different location than looking over the neighborhood.
exists e1 x1 x2 x3.(n_wall(x3) & n_city(x2) & n_guard(x1) & past(e1,x3) & at(e1,x2) & Actor(e1,x1) & v_look(e1))
exists e1 x1 x2.(n_neighborhood(x2) & n_policeman(x1) & over(e1,x2) & Actor(e1,x1) & v_look(e1))