A construction worker works is welding.
Nobody is working
If nobody is working then it's impossible that a worker works.
exists e1 e2 x1 x2 x3.(Actor(e2,x1) & v_weld(e2) & Actor(e1,x3) & v_work(e1) & (x1 = x3) & n_worker(x1) & of(x1,x2) & n_construction(x2))
-exists e1 x1.(Actor(e1,x1) & v_work(e1) & n_person(x1))