Two girls talking while sitting on the stairs.
Two girls are happily talking.
Two girls talking while sitting on the stairs does not necessary that they are happily talking.
exists e2 e1 x1 x2 x3.(n_stair(x3) & a_topic(x1) & while(e1,e2) & on(e2,x3) & Actor(e2,x2) & v_sit(e2) & Actor(e1,x2) & v_talk(e1) & (x1 = x2) & n_girl(x1) & card_eq_2(x1))
exists e1 s1 x1.(a_happily(s1) & Manner(e1,s1) & Actor(e1,x1) & v_talk(e1) & n_girl(x1) & card_eq_2(x1))