A mannequin behind a blue car.
There is nothing behind the blue car.
A mannequin is not nothing.
exists s1 x1 x2.(a_topic(x1) & behind(x1,x2) & n_car(x2) & a_blue(s1) & Theme(s1,x2) & n_mannequin(x1))
exists p1 s1 x1 x3.(n_car(x3) & a_blue(s1) & Theme(s1,x3) & -exists x2.((x1 = x2) & behind(x2,x3) & n_thing(x2)))