Two boys are playing on the ground.
The two boys are playing on the sofa.
Sofa and ground are not the same thing.
exists e1 x1 x2.(n_ground(x2) & on(e1,x2) & Actor(e1,x1) & v_play(e1) & n_boy(x1) & card_eq_2(x1))
exists e1 x1 x2.(n_sofa(x2) & n_boy(x1) & card_eq_2(x1) & on(e1,x2) & Actor(e1,x1) & v_play(e1))