proposition: Lemma enum_valK_in x0 A Ax0 : cancel enum_val (@enum_rank_in x0 A Ax0).
proof: Proof. move=> x; apply: ord_inj; rewrite insubdK; last first. by rewrite cardE [_ \in _]index_mem mem_nth // -cardE. by rewrite index_uniq ?enum_uniq // -cardE. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)