Proof using.
intros m c; generalize m; elim c; clear c m; simpl in |- *; auto.
intros m; elim m; simpl in |- *; auto.
intros (a, l1) l Rec m H; simpl in |- *.
case (number_of_occurrences_permutation_ex A eqA_dec m a);
intros m1 (Hm1, Hm2).
rewrite
permutation_length
with
(1 :=
encode_permutation_val _ eqA_dec _ _ ((a, l1) :: l) Hm1).
rewrite encode_app; auto.
rewrite length_app; auto.
rewrite length_encode_nId.
rewrite encode_cons_inv; auto.
rewrite Rec; simpl in |- *; auto.
rewrite <-
fold_plus_split
with
(f :=
fun b : A * list bool =>
number_of_occurrences eqA_dec (fst b) m * length (snd b))
(c := number_of_occurrences eqA_dec a m * length l1).
apply f_equal2 with (f := plus); auto.
cut (forall l2, ~ In (a, l2) l).
elim l; simpl in |- *; auto.
intros (a2, l2) l3; simpl in |- *; intros Rec1 H4.
rewrite <-
fold_plus_split
with
(c := number_of_occurrences eqA_dec a2 m1 * length l2)
(f :=
fun b : A * list bool =>
number_of_occurrences eqA_dec (fst b) m1 * length (snd b)).
rewrite <-
fold_plus_split
with
(c := number_of_occurrences eqA_dec a2 m * length l2)
(f :=
fun b : A * list bool =>
number_of_occurrences eqA_dec (fst b) m * length (snd b)).
apply f_equal2 with (f := plus); auto.
2: apply Rec1; auto.
2: intros l0; red in |- *; intros H0; case (H4 l0); auto.
2: intros l2; red in |- *; intros H0;
case unique_key_in with (1 := H) (a := a) (b2 := l2);
auto.
2: apply unique_key_inv with (1 := H); auto.
apply f_equal2 with (f := mult); auto.
apply
trans_equal
with
(2 := number_of_occurrences_permutation _ eqA_dec _ _ a2
(permutation_sym _ _ _ Hm1)).
rewrite number_of_occurrences_app.
replace
(number_of_occurrences eqA_dec a2
(id_list a (number_of_occurrences eqA_dec a m))) with 0;
auto.
cut (a2 <> a).
elim (number_of_occurrences eqA_dec a m); simpl in |- *; auto.
intros n H0 H1; case (eqA_dec a2 a); simpl in |- *; auto.
intros e; case H1; auto.
red in |- *; intros H0; case (H4 l2); left;
apply f_equal2 with (f := pair (A:=A) (B:=list bool));
auto.
Qed.
Definition weight m c := length (encode eqA_dec c m).

Theorem weight_permutation :
forall m c1 c2,
unique_prefix c1 -> permutation c1 c2 -> weight m c1 = weight m c2.