A firefighter is working at a fire.
The firefighter is at someone's house.
Just because the firefighter is working at a fire doesn't mean he's at someone's house.
exists e1 x1 x2.(at(e1,x2) & n_fire(x2) & Actor(e1,x1) & v_work(e1) & n_firefighter(x1))
exists p1 x1.(n_firefighter(x1) & exists x2 x3.(at(x1,x3) & n_house(x3) & of(x3,x2) & n_person(x2)))