People are walking by a building.
There are people walking.
The people that are walking are walking by a building
exists e1 x1 x2.(by(e1,x2) & n_building(x2) & Actor(e1,x1) & v_walk(e1) & n_people(x1))
exists p1 x1 e1 x2 x3.((x1 = x2) & Actor(e1,x3) & v_walk(e1) & (x2 = x3) & n_people(x2))