Two boys are talking while one is sitting on a mule.
Two boys are riding horses.
Mules and horses are two different animals.
exists e1 p1 x1.(exists e2 x2 x3.(on(e2,x3) & n_mule(x3) & Actor(e2,x2) & v_sit(e2) & n_thing(x2) & card_eq_1(x2)) & while(e1,p1) & Actor(e1,x1) & v_talk(e1) & n_boy(x1) & card_eq_2(x1))
exists e1 x1 x2.(Theme(e1,x2) & Actor(e1,x1) & v_ride(e1) & n_horse(x2) & n_boy(x1) & card_eq_2(x1))