A child plays at a playground.
A child is playing.
in a both sentence child and playing are different.
exists e1 x1 x2.(at(e1,x2) & n_playground(x2) & Actor(e1,x1) & v_play(e1) & n_child(x1))
exists e1 x1.(Actor(e1,x1) & v_play(e1) & n_child(x1))