intros. simpl in |- *. do 3 rewrite BV_to_nat_app2. simpl in |- *.
rewrite mult_plus_distr2.
rewrite
(mult_plus_distr2 (BV_to_nat V2) (BV_to_nat (truncbv V1 n))
(power2 (lengthbv (truncbv V1 n)) * 1)).
rewrite <- H. clear H. elim plus_n_O.
rewrite highs_is_strip. rewrite highs_is_strip.
rewrite (length_trunc bool). rewrite (length_strip bool).
rewrite (length_app bool). rewrite (length_strip bool).
rewrite (length_strip bool). rewrite length_abit.
rewrite length_R1. rewrite (plus_comm (size - 1)).
replace (1 + (size - 1)) with size.
rewrite minus_minus_lem2. rewrite length_BV_full_adder_sum.
rewrite length_R2. rewrite (strip_app bool).
rewrite BV_to_nat_app2. rewrite (strip_strip bool).
rewrite (length_strip bool). rewrite (length_strip bool).
rewrite length_R1. rewrite BV_to_nat_app2.
simpl in |- *. rewrite minus_Sn_m.
rewrite (minus_le_O (size - S n) (size - 1)).
simpl in |- *. rewrite minus_minus_lem2.
rewrite (strip_O bool). rewrite (length_strip bool).
rewrite length_R1. rewrite minus_minus_lem2.
replace (power2 n + power2 n) with (power2 (S n)).
replace (power2 n * 1) with (power2 n).
rewrite <- (mult_assoc_reverse (power2 (S n))).
rewrite <- power2_plus. simpl in |- *. rewrite <- power2_eq2. rewrite <- power2_eq2.
replace (S (n + (size - 1))) with (n + size).
repeat rewrite plus_assoc_reverse.
replace
(power2 n * BV_to_nat (abit (BV_full_adder_sum (R2 n) V2 false) 0) +
(power2 (S n) * BV_to_nat (stripbv (BV_full_adder_sum (R2 n) V2 false) 1) +
power2 (n + size) * bool_to_nat (BV_full_adder_carry (R2 n) V2 false)))
with (power2 n * BV_to_nat (R2 n) + BV_to_nat V2 * power2 n).
trivial with arith. rewrite plus_assoc. rewrite <- highs_is_strip.
unfold abit in |- *. unfold elemlist in |- *. rewrite (strip_O bool).
rewrite <- lowbit_is_trunc. rewrite BV_nat_lem1. rewrite power2_plus.
rewrite (mult_assoc_reverse (power2 n)). rewrite <- mult_plus_distr2.
replace size with (lengthbv (BV_full_adder_sum (R2 n) V2 false)).
replace (bool_to_nat (BV_full_adder_carry (R2 n) V2 false)) with
(BV_to_nat (consbv (BV_full_adder_carry (R2 n) V2 false) nilbv)).
rewrite <- BV_to_nat_app2.
replace
(appbv (BV_full_adder_sum (R2 n) V2 false)
(consbv (BV_full_adder_carry (R2 n) V2 false) nilbv)) with
(BV_full_adder (R2 n) V2 false).
rewrite BV_full_adder_ok.
rewrite mult_plus_distr2. rewrite mult_plus_distr2.
simpl in |- *. elim mult_n_O. elim plus_n_O. rewrite (mult_sym (BV_to_nat V2)).
trivial with arith. unfold BV_full_adder in |- *. trivial with arith.
simpl in |- *. elim plus_n_O. trivial with arith. rewrite length_BV_full_adder_sum; auto with arith.
rewrite length_R2; auto with arith. rewrite length_BV_full_adder_sum; auto with arith.
rewrite length_R2; auto with arith. rewrite length_R2; auto with arith.
apply (not_nil bool); auto with arith. rewrite length_BV_full_adder_sum; auto with arith.
rewrite length_R2; auto with arith. rewrite length_R2; auto with arith.
replace (S (n + (size - 1))) with (S n + (size - 1)).
replace (S n + (size - 1)) with (n + S (size - 1)).
rewrite minus_Sn_m. simpl in |- *. elim minus_n_O. trivial with arith.
auto with arith. rewrite plus_comm. simpl in |- *. rewrite plus_comm. trivial with arith.
simpl in |- *. trivial with arith. rewrite mult_sym. simpl in |- *. elim plus_n_O.
trivial with arith. auto with arith. exact H1. exact H1. rewrite length_R1; auto with arith.
exact H1. apply le_minus_minus. auto with arith. exact H0. exact H1.
rewrite length_R1. auto with arith. exact H1. rewrite length_R1; auto with arith.
exact H1.
rewrite length_R2; auto with arith. exact H0. simpl in |- *. rewrite minus_Sn_m.
auto with arith. auto with arith. exact H1. rewrite length_BV_full_adder_sum; auto with arith.
unfold lt in |- *. rewrite length_R2. auto with arith. exact H1. transitivity size; auto with arith.
rewrite length_BV_full_adder_sum; auto with arith. rewrite length_R2; auto with arith.
rewrite length_R2; auto with arith. rewrite length_R1; auto with arith.
rewrite (length_app bool). rewrite (length_strip bool).
rewrite length_R1; auto with arith. rewrite length_abit. rewrite plus_comm.
simpl in |- *. rewrite minus_Sn_m. simpl in |- *. elim minus_n_O. apply minus_le_lem2. auto with arith.
rewrite length_BV_full_adder_sum; auto with arith. rewrite length_R2; auto with arith.
rewrite length_R2; auto with arith. rewrite length_R1; auto with arith.
replace (length V1) with (lengthbv V1); auto with arith.
rewrite length_V1_size. exact H1. exact H1.
Qed.
(****************************************************************)
(* Finalement on prouve le cas general de l'invariant: *)

(* Specifications: *)
Lemma Invariant :
forall t : nat,
t <= size ->
BV_to_nat (appbv (stripbv (R1 t) (size - t)) (R2 t)) =
BV_to_nat V2 * BV_to_nat (truncbv V1 t).