A surfer riding the wave.
A person riding a wave for a competition.
Riding a wave does not imply it being a competition.
exists e1 x1 x2 x3.(n_wave(x3) & a_topic(x1) & Theme(e1,x3) & Actor(e1,x2) & v_ride(e1) & (x1 = x2) & n_surfer(x1))
exists e1 x1 x2 x3 x4.(a_topic(x1) & for(e1,x4) & n_competition(x4) & Theme(e1,x3) & Actor(e1,x2) & v_ride(e1) & n_wave(x3) & (x1 = x2) & n_person(x1))