Definition binop_stable cenv op a1 a2 : bool :=
match op with
  | Cop.Oadd => match Cop.classify_add (typeof a1) (typeof a2) with
                    | Cop.add_case_pi t _ => complete_type cenv t
                    | Cop.add_case_ip _ t => complete_type cenv t
                    | Cop.add_case_pl t => complete_type cenv t
                    | Cop.add_case_lp t => complete_type cenv t
                    | Cop.add_default => true
            end
  | Cop.Osub => match Cop.classify_sub (typeof a1) (typeof a2) with
                    | Cop.sub_case_pi t _ => complete_type cenv t
                    | Cop.sub_case_pl t => complete_type cenv t
                    | Cop.sub_case_pp t => complete_type cenv t
                    | Cop.sub_default => true
            end
  | _ => true
  end.

Lemma tycontext_eqv_symm: forall Delta Delta', tycontext_eqv Delta Delta' -> tycontext_eqv Delta' Delta.