A boy plays in the sand.
A boy is building a castle in the sand.
You can not infer he is building a castle.
exists e1 x1 x2.(n_sand(x2) & in(e1,x2) & Actor(e1,x1) & v_play(e1) & n_boy(x1))
exists e1 x1 x2 x3.(n_sand(x3) & in(e1,x3) & Theme(e1,x2) & Actor(e1,x1) & v_build(e1) & n_castle(x2) & n_boy(x1))