proposition: Lemma big1_seq (I : eqType) r (P : pred I) F : (forall i, P i && (i \in r) -> F i = 1) -> \big[*%M/1]_(i <- r | P i) F i = 1.
proof: Proof. by move=> eqF1; rewrite big_seq_cond big_andbC big1. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq path) mathcomp(div fintype tuple finfun)