A person runs with a dog.
A boy runs down the beach with his dog.
A person is running his dog. It doesn't necessarily need to be a boy. Also, it could be anywhere, not just the beach.
exists e1 x1 x2.(with(e1,x2) & n_dog(x2) & Actor(e1,x1) & v_run(e1) & n_person(x1))
exists e1 x1 x2 x3.(n_dog(x3) & of(x3,x2) & n_male(x2) & n_beach(x2) & down(e1,x2) & with(x2,x3) & Actor(e1,x1) & v_run(e1) & n_boy(x1))