A redheaded boy swimming underwater.
A person swimming with a friend underwater
The boy swimming is not implied to be swimming with his friend.
exists s1 x1 x2 x3.(a_topic(x1) & n_underwater(x1) & of(x1,x3) & n_swimming(x3) & of(x1,x2) & n_boy(x2) & a_redheaded(s1) & Theme(s1,x1))
exists x1 x2 x3 x4.(a_topic(x1) & with(x1,x3) & n_underwater(x3) & of(x3,x4) & n_friend(x4) & Time(x1,x2) & n_swimming(x2) & n_person(x1))