A dog jumps over an obstacle.
A cat jumps over the obstacle.
There can be either a dog or a cat.
exists e1 x1 x2.(over(e1,x2) & n_obstacle(x2) & Actor(e1,x1) & v_jump(e1) & n_dog(x1))
exists e1 x1 x2.(n_obstacle(x2) & over(e1,x2) & Actor(e1,x1) & v_jump(e1) & n_cat(x1))