A black dog is chasing another black dog.
Nothing is chasing.
Nothung can't be chasing if the dog is chasing.
exists e1 s1 s2 s3 x1 x2.(Theme(e1,x2) & Actor(e1,x1) & v_chase(e1) & n_dog(x2) & a_black(s3) & Theme(s3,x2) & -(x2 = x1) & n_dog(x1) & n_dog(x1) & a_black(s2) & Theme(s2,x1) & a_black(s1) & Theme(s1,x1))
-exists e1 x1.(Actor(e1,x1) & v_chase(e1) & n_thing(x1))