A surfer on a roiling wave.
A man surfing
Man surfing is mentioned in both sentences
exists e1 x1 x2.(a_topic(x1) & on(x1,x2) & n_wave(x2) & Actor(e1,x2) & v_roil(e1) & n_surfer(x1))
exists x1 x2.(a_topic(x1) & n_surfing(x1) & of(x1,x2) & n_man(x2))