The dog is running in a field.
The dog is chasing a squirrel.
Dogs can run a field for many reasons.  They are not always chasing a squirrel.
exists e1 x1 x2.(n_dog(x1) & in(e1,x2) & n_field(x2) & Actor(e1,x1) & v_run(e1))
exists e1 x1 x2.(n_dog(x1) & Theme(e1,x2) & Actor(e1,x1) & v_chase(e1) & n_squirrel(x2))