Three people dancing in the subway.
Nobody is dancing.
Either three people are dancing, or nobody is dancing at all.
exists e1 x1 x2 x3.(n_subway(x3) & a_topic(x1) & in(e1,x3) & Actor(e1,x2) & v_dance(e1) & (x1 = x2) & n_people(x1) & card_eq_3(x1))
-exists e1 x1.(Actor(e1,x1) & v_dance(e1) & n_person(x1))