A girl and a boy laughing
A brother and sister are laughing.
The girl and boy did not have to be brother and sister.
exists e1 s1 x1 x2 x3.(a_topic(s1) & subset_of(x2,s1) & Actor(e1,x3) & v_laugh(e1) & (x2 = x3) & n_boy(x2) & subset_of(x1,s1) & n_girl(x1))
exists e1 x1 x2 x3.(Actor(e1,x1) & v_laugh(e1) & n_sister(x3) & n_brother(x2) & subset_of(x3,x1) & subset_of(x2,x1))