Some construction workers are taking a break.
A librarian returns books to the shelves.
They are either construction workers, or a librarian. They cannot be taking a break and returning books to the shelves at the same time.
exists e1 x1 x2 x3.(Theme(e1,x3) & Actor(e1,x1) & v_take(e1) & n_break(x3) & n_worker(x1) & of(x1,x2) & n_construction(x2))
exists s1 x1 x2 x3.(n_shelf(x3) & a_topic(x1) & to(x1,x3) & n_book(x1) & of(x1,x2) & n_return(x2) & a_librarian(s1) & Theme(s1,x1))