Section FoldRight.
Variables (T : Type) (R : Type) (f : T -> R -> R) (z0 : R).
Fixpoint foldr s := if s is x :: s' then f x (foldr s') else z0.
End FoldRight.

Lemma mem_iota m n i : (i \in iota m n) = (m <= i) && (i < m + n).