a surfer rides the wave.
A person is surfing.
Surfer is a person
exists e1 x1 x2.(n_wave(x2) & Theme(e1,x2) & Actor(e1,x1) & v_ride(e1) & n_surfer(x1))
exists e1 x1.(Actor(e1,x1) & v_surf(e1) & n_person(x1))