Two children are playing on a bicycle.
There are no children.
Children is different than no children.
exists e1 x1 x2.(on(e1,x2) & n_bicycle(x2) & Actor(e1,x1) & v_play(e1) & n_child(x1) & card_eq_2(x1))
exists p1 x1.-exists x2.((x1 = x2) & n_child(x2))