A brown dog in a field.
A dog is in a field.
Both sentence are talking about dog.
exists s1 x1 x2.(a_topic(x1) & in(x1,x2) & n_field(x2) & n_dog(x1) & a_brown(s1) & Theme(s1,x1))
exists p1 x1.(exists x2.(in(x1,x2) & n_field(x2)) & n_dog(x1))