A couple smiling while sitting.
the couple was waiting for their friends
You can not infer they are waiting.
exists e2 e1 x1 x2.(a_topic(x1) & while(e1,e2) & Actor(e2,x2) & v_sit(e2) & Actor(e1,x2) & v_smile(e1) & (x1 = x2) & n_couple(x1))
exists e1 x1 x2.(n_friend(x2) & of(x2,x1) & n_thing(x1) & n_couple(x1) & for(e1,x2) & Actor(e1,x1) & v_wait(e1))