Two boys are playing ping-pong.
Two girls play tennis.
The children cannot be boys and girls at the same time.  Ping-pong is different than tennis.
exists e1 x1 x2.(Theme(e1,x2) & Actor(e1,x1) & v_play(e1) & n_ping-pong(x2) & n_boy(x1) & card_eq_2(x1))
exists e1 x1 x2.(Theme(e1,x2) & Actor(e1,x1) & v_play(e1) & n_tennis(x2) & n_girl(x1) & card_eq_2(x1))