a man sleeps on a desk.
A man is sleeping at work.
Although the man is at a desk, he may not be at work at all.
exists e1 x1 x2.(on(e1,x2) & n_desk(x2) & Actor(e1,x1) & v_sleep(e1) & n_man(x1))
exists e1 x1 x2.(at(e1,x2) & n_work(x2) & Actor(e1,x1) & v_sleep(e1) & n_man(x1))