proposition: Lemma seq2_ind (T1 T2 : Type) (P : seq T1 -> seq T2 -> Prop) : P [::] [::] -> (forall x1 x2 s1 s2, P s1 s2 -> P (x1 :: s1) (x2 :: s2)) -> forall s1 s2, size s1 = size s2 -> P s1 s2.
proof: Proof. move=> HP IHP. elim=> [|x1 l1 IH1]; case=> // x2 l2 /= Hs. apply: IHP; apply: IH1. by move/eqnP: Hs=> /= /eqnP. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype fintype finfun ssrnat seq) mathcomp(choice ssralg poly polydiv mxpoly matrix bigop) mathcomp(mxalgebra perm fingroup tuple) mxstructure dvdring