A swimmer in a pool swimming on their back
A woman is doing the backstroke in a pool.
A swimmer swimming may not be a woman and may not be doing the backstroke even if they are on their back in the pool.
exists x1 x2 x3 x4.(a_topic(x1) & in(x1,x2) & on(x2,x4) & n_back(x4) & of(x4,x1) & n_thing(x1) & n_swimming(x2) & of(x2,x3) & n_pool(x3) & n_swimmer(x1))
exists e1 x1 x2 x3.(n_backstroke(x2) & Theme(e1,x2) & Actor(e1,x1) & v_do(e1) & in(x2,x3) & n_pool(x3) & n_woman(x1))