Four people and the sun.
Four people and the moon.
The moon and the sun are two different things.
exists s1 x1 x2.(n_sun(x2) & a_topic(s1) & subset_of(x2,s1) & subset_of(x1,s1) & n_people(x1) & card_eq_4(x1))
exists s1 x1 x2.(n_moon(x2) & a_topic(s1) & subset_of(x2,s1) & subset_of(x1,s1) & n_people(x1) & card_eq_4(x1))