A surfer is on a wave.
A surfer relaxes on the beach.
The surfer would not be on a wave if they were relaxing on a beach because they could not be relaxing while they were surfing on a wave.
exists p1 x1.(exists x2.(on(x1,x2) & n_wave(x2)) & n_surfer(x1))
exists e1 x1 x2.(n_beach(x2) & on(e1,x2) & Actor(e1,x1) & v_relax(e1) & n_surfer(x1))