Opaque OneMinus_e.
(** Def 4 of (Rose) *)
Definition Div2_e : Cobham :=
Rec2
Zero
(Proj 2 0)
(Proj 1 0).

Lemma Div2_correct : forall l,
bs2nat (Sem Div2_e l) = div2 (bs2nat (hd nil l)).