proposition: Lemma big_mkcond I r (P : pred I) F : \big[*%M/1]_(i <- r | P i) F i = \big[*%M/1]_(i <- r) (if P i then F i else 1).
proof: Proof. by rewrite unlock; elim: r => //= i r ->; case P; rewrite ?mul1m. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq path) mathcomp(div fintype tuple finfun)