A woman and two children sightseeing.
Nobody is sightseeing.
It is impossible that nobody is sightseeing because a woman and two children are sightseeing.
exists e1 s1 x1 x2 x3.(a_topic(s1) & Actor(e1,x3) & v_sightsee(e1) & (s1 = x3) & subset_of(x2,s1) & n_child(x2) & card_eq_2(x2) & subset_of(x1,s1) & n_woman(x1))
-exists e1 x1.(Actor(e1,x1) & v_sightsee(e1) & n_person(x1))