Local Open Scope logic.
Fixpoint power_later (n:nat) P :=
match n with
| 0%nat => P
| S n' => later (power_later n' P)
end
.
Ltac power_normalize :=
repeat (
try rewrite -> power_later_andp;
try rewrite -> power_later_sepcon;
try rewrite <- power_later_TT)
.

Lemma power_later_erase: forall n P Q R, P * Q |-- R -> power_later n P * Q |-- power_later n R.