Hint Resolve check_rval_wt check_lval_wt: ty.
Hint Extern 1 (wt_expr _ _ _) => (unfold wt_expr; simpl): ty.

Lemma retype_expr_sound:
forall a a', retype_expr ce e a = OK a' -> wt_expr ce e a'
with retype_exprlist_sound:
forall al al', retype_exprlist ce e al = OK al' -> wt_exprlist ce e al'.