A man is riding on a surfboard.
The man is in a boat behind a truck.
If a man is riding on a surfboard, he is not likely to also be in a boat.
exists e1 x1 x2.(on(e1,x2) & n_surfboard(x2) & Actor(e1,x1) & v_ride(e1) & n_man(x1))
exists p1 x1.(n_man(x1) & exists x2 x3.(in(x1,x2) & behind(x2,x3) & n_truck(x3) & n_boat(x2)))