A man surfing on a big green wave.
A man is participating in a surfing contest.
Not all surfers are competing in a contest; the man could be surfing for pleasure.
exists e1 s1 s2 x1 x2 x3.(a_topic(x1) & on(e1,x3) & n_wave(x3) & a_green(s2) & Theme(s2,x3) & a_big(s1) & Theme(s1,x3) & Actor(e1,x2) & v_surf(e1) & (x1 = x2) & n_man(x1))
exists e1 x1 x2 x3.(in(e1,x2) & n_contest(x2) & of(x2,x3) & n_surfing(x3) & Actor(e1,x1) & v_participate(e1) & n_man(x1))