Young sheep in the grass.
Nothing in the grass.
If there are young sheep in the grass, there can not also be nothing.
exists s1 x1 x2.(n_grass(x2) & a_topic(x1) & in(x1,x2) & n_sheep(x1) & a_young(s1) & Theme(s1,x1))
exists x2.(n_grass(x2) & -exists x1.(a_topic(x1) & in(x1,x2) & n_thing(x1)))