proposition: Lemma size_rhalf_cleaner_rec n : size (rhalf_cleaner_rec n) = n.
proof: Proof. case: n => //= n. by rewrite /ndup /= size_map size_zip size_half_cleaner_rec minnn. Qed.
imports: mathcomp(all_ssreflect perm algebra.zmodp) mathcomp(zify) more_tuple nsort