Definition loop1y_ret_assert (Inv : environ -> mpred) :=
  {| RA_normal := Inv; RA_break := FF; RA_continue := Inv; RA_return := FF |}.Definition for_ret_assert (I: environ->mpred) (Post: ret_assert) :=
 match Post with 
  {| RA_normal := _; RA_break := _; RA_continue := _; RA_return := r |} =>
  {| RA_normal := I; RA_break := FF; RA_continue := I; RA_return := r |}
 end.Ltac simpl_ret_assert := 
 cbn [RA_normal RA_break RA_continue RA_return 
      normal_ret_assert overridePost loop1_ret_assert
      loop2_ret_assert function_body_ret_assert frame_ret_assert
      switch_ret_assert loop1x_ret_assert loop1y_ret_assert
      for_ret_assert loop_nocontinue_ret_assert].

Lemma liftx2_liftx1: forall {A1 A2 B} f (x: A1), @liftx (Tarrow A1 (Tarrow A2 (LiftEnviron B))) f (@liftx (LiftEnviron A1) x) = @liftx (Tarrow A2 (LiftEnviron B)) (f x).