proposition: Lemma big_const_seq : forall r (P : pred I) x, \big[op/idx]_(i <- r | P i) x === iter (count P r) (op x) idx.
proof: Proof. move=> r P x; elim: r; try reflexivity; move=> i r //=. by case: (P i); move=> Heq; rewrite -> Heq; reflexivity. Qed.
imports: ssreflect ssrbool ssrfun eqtype ssrnat seq div choice fintype finfun paths Setoid Morphisms OperationClasses bigops