Sled dogs pull a sled through a snowy forest.
Nothing is pulling
Nothing can refer to anything and you either are pulling of not, you can not be doing both.
exists e1 s1 s2 x1 x2 x3.(through(e1,x3) & n_forest(x3) & a_snowy(s2) & Theme(s2,x3) & Theme(e1,x2) & Actor(e1,x1) & v_pull(e1) & n_sled(x2) & n_dog(x1) & a_sled(s1) & Theme(s1,x1))
-exists e1 x1.(Actor(e1,x1) & v_pull(e1) & n_thing(x1))