Two young girls on a playground.
They are sisters.
girls  doesn't imply sisters.
exists s1 x1 x2.(a_topic(x1) & on(x1,x2) & n_playground(x2) & n_girl(x1) & a_young(s1) & Theme(s1,x1) & card_eq_2(x1))
exists p1 x1.(n_thing(x1) & exists x2.((x1 = x2) & n_sister(x2)))