Firefighters hard at work.
The firefighters are fighting a fire.
Firefighters hard at work may not be fighting a fire.
exists s1 x1 x2.(at(s1,x2) & n_work(x2) & Theme(s1,x1) & a_hard(s1) & n_firefighter(x1))
exists e1 x1 x2.(n_firefighter(x1) & Theme(e1,x2) & Actor(e1,x1) & v_fight(e1) & n_fire(x2))