a surfer rides the wave.
The surfer went home after the water was calm.
The surfer either rides the wave or goes home, but they cannot do both.
exists e1 x1 x2.(n_wave(x2) & Theme(e1,x2) & Actor(e1,x1) & v_ride(e1) & n_surfer(x1))
exists e1 p1 x1 x2 x3.(n_water(x3) & n_surfer(x1) & exists s1.(Theme(s1,x3) & a_calm(s1)) & after(e1,p1) & Theme(e1,x2) & Actor(e1,x1) & v_go(e1) & n_home(x2))