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 econdition_sound: forall r1 r2 r3 a, econdition r1 r2 r3 = OK a -> wt_expr ce e r1 -> wt_expr ce e r2 -> wt_expr ce e r3 -> wt_expr ce e a.