Corollary check_rval_wt:
  forall a x, wt_expr ce e a -> check_rval a = OK x -> wt_rvalue ce e a.Corollary check_lval_wt:
  forall a x, wt_expr ce e a -> check_lval a = OK x -> wt_lvalue ce e a.

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'.