proposition: Lemma big1 I r (P : pred I) F : (forall i, P i -> F i = 1) -> \big[*%M/1]_(i <- r | P i) F i = 1.
proof: Proof. by move/(eq_bigr _)->; apply: big1_eq. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq path) mathcomp(div fintype tuple finfun)