A dog is digging in the sand beneath some grass.
A dog is sleeping by a fire.
either digging and sleeping are cannot be same.
exists e1 x1 x2 x3.(n_sand(x2) & beneath(e1,x3) & n_grass(x3) & in(e1,x2) & Actor(e1,x1) & v_dig(e1) & n_dog(x1))
exists e1 x1 x2.(by(e1,x2) & n_fire(x2) & Actor(e1,x1) & v_sleep(e1) & n_dog(x1))