A worker walking down the street.
There is nobody on the street.
a worker refers to one person and not nobody
exists e1 x1 x2 x3.(n_street(x3) & a_topic(x1) & down(e1,x3) & Actor(e1,x2) & v_walk(e1) & (x1 = x2) & n_worker(x1))
exists p1 x1 x3.(n_street(x3) & -exists x2.((x1 = x2) & on(x2,x3) & n_person(x2)))