Hint Rewrite @evalCR_zero: Recurrence.

(** Basic theorem, show how to unfold CReval *)
Lemma evalCR_step: forall
`{Ring R}
(cr': CR) (r: R) (bop: R -> R -> R) (n: nat),
(recurCR r bop cr') # (S n) =
bop ((recurCR r bop cr') # n)
((evalAtIx (CR_to_BR cr')) # (S n)).