Section Sk.
Hypothesis k:nat.
Hypothesis Base_k: k<>0.
Inductive Base: (nat*(list nat))->Prop :=
| Base_intro s
(Base_a0':fst s = S O)
(Base_a:forall i, ai i s = if Nat.ltb i (k*2) then 2^(k*2-i) else O)
(Base_l:to_l s = k*2+1):
Base s.
Ltac pose_Heb Heb Hl e2 Heb2 rw :=
epose proof (embanked_batch_precond'' Heb Hl _ _) as tmp;
edestruct tmp as [e2 Heb2]; clear tmp;
rewrite rw in Heb2;
cbn in Heb2.
Ltac ex_Heb e Heb :=
exists e; eexists;
split;
[ apply Heb | idtac ].
Ltac pose_eb_len Heb Hl0 Hl :=
pose proof (embanked_batch_len Heb) as Hl;
rewrite Hl0 in Hl; symmetry in Hl.
Ltac pose_eb_a0_a1 Heb Ha0 Ha1 rw :=
destruct (embanked_batch_a0_a1 Heb) as [Ha0 Ha1];
rewrite rw in Ha0,Ha1;
cbn in Ha0,Ha1.

Lemma mod_mod' a b c:
a mod c = a mod (b*c) mod c.