A man on a surfboard rides the waves.
A man is surfing.
Riding the waves on surfboard means surfing.
exists e1 x1 x2 x3.(n_wave(x3) & Theme(e1,x3) & Actor(e1,x1) & v_ride(e1) & on(x1,x2) & n_surfboard(x2) & n_man(x1))
exists e1 x1.(Actor(e1,x1) & v_surf(e1) & n_man(x1))