One boy hoists another boy up on his back.
A boy is giving another boy a piggy back ride.
One can hoist a person on their back without it being a piggy back ride.
exists e1 s1 x1 x2 x3.(on(e1,x3) & n_back(x3) & of(x3,x2) & n_male(x2) & a_up(s1) & Manner(e1,s1) & Theme(e1,x2) & Actor(e1,x1) & v_hoist(e1) & n_boy(x2) & -(x2 = x1) & n_boy(x1) & n_boy(x1) & card_eq_1(x1))
exists e1 x1 x2 x3 x4.(back(e1,x4) & n_piggy(x4) & Recipient(e1,x3) & Theme(e1,x2) & Actor(e1,x1) & v_give(e1) & n_boy(x3) & -(x3 = x1) & n_boy(x1) & n_boy(x1) & n_ride(x2))