Hint Constructors PPO.

Lemma same_rank_same_ppo_rule vv ff cc f lp (t : term vv ff cc) rk rk':
rk f = rk' f ->
(forall g, g ∈ (functions_of_term t) -> rk g = rk' g) ->
PPO rk t (fapply f (map (@term_from_pattern _ _ _) lp)) ->
PPO rk' t (fapply f (map (@term_from_pattern _ _ _) lp)).