Two friends bike down a hill.
Two boys on a hill.
Not all friends are boys.
exists x1 x2 x3.(a_topic(x1) & down(x1,x3) & n_hill(x3) & n_bike(x1) & of(x1,x2) & n_friend(x2) & card_eq_2(x1))
exists x1 x2.(a_topic(x1) & on(x1,x2) & n_hill(x2) & n_boy(x1) & card_eq_2(x1))