proposition: Lemma otake_cat (T : Type) (s1 s2 : seq T) : otake (s1 ++ s2) = otake s1 ++ if odd (size s1) then etake s2 else otake s2.
proof: Proof. by case: s1 => // a l; rewrite /= if_neg etake_cat. Qed.
imports: mathcomp(all_ssreflect perm algebra.zmodp) mathcomp(zify)