A artist is at work making a sculpture.
A artist is not at work
If he is at work, it can't be that he is not at work.
exists e1 p1 x1 x2.(for(p1,e1) & Theme(e1,x2) & Actor(e1,x1) & v_make(e1) & n_sculpture(x2) & exists x3.(at(x1,x3) & n_work(x3)) & n_artist(x1))
exists x1.(-exists p1 x2.(at(x1,x2) & n_work(x2)) & n_artist(x1))