A person is riding a surfboard on a wave.
A person is riding a surfboard falls off when a wave hits.
A person riding a surfboard on a wave does not mean the person falls off when the wave hits.
exists e1 x1 x2 x3.(on(e1,x3) & n_wave(x3) & Theme(e1,x2) & Actor(e1,x1) & v_ride(e1) & n_surfboard(x2) & n_person(x1))
exists e1 e2 p1 s1 x1 x2 x3.(exists e3 x4.(Actor(e3,x4) & v_hit(e3) & n_wave(x4)) & when(e2,p1) & a_off(s1) & Manner(e2,s1) & Actor(e2,x1) & v_fall(e2) & Theme(e1,x3) & Actor(e1,x2) & v_ride(e1) & n_surfboard(x3) & (x1 = x2) & n_person(x1))