Parameter expr_eq : option expr -> option expr -> bool.

(* Specifications: *)
Axiom expr_eq_correct : forall x y, expr_eq x y = true -> x = y.
Definition c_option_expr_type :=
({| Expr.Impl := option expr
; Expr.Eqb := expr_eq
; Expr.Eqb_correct := expr_eq_correct |}).