A boy surfs on a wave.
The boy snowboards.
SNOWBOARDS HAVE NOTHING TO DO WITH SURFS
exists e1 x1 x2.(on(e1,x2) & n_wave(x2) & Actor(e1,x1) & v_surf(e1) & n_boy(x1))
exists x1 x2.(n_snowboard(x1) & of(x1,x2) & n_boy(x2) & a_topic(x1))