proposition: Lemma decn_inP : {in D, forall i, i.+1 \in D -> f i > f i.+1} -> {in D &, {mono f : i j /~ i <= j}}.
proof: Proof. by move=> f_dec; apply/le_nmono_in/nhomo_ltn_lt_in. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)