A dog jumps over an obstacle.
A dog jumps over the skateboard.
The obstacle the dog is jumping may not be a skateboard.
exists e1 x1 x2.(over(e1,x2) & n_obstacle(x2) & Actor(e1,x1) & v_jump(e1) & n_dog(x1))
exists e1 x1 x2.(n_skateboard(x2) & over(e1,x2) & Actor(e1,x1) & v_jump(e1) & n_dog(x1))