Definition nonlocal (Q: environ->mpred) := True.Ltac check_nonlocal :=
  match goal with
  |  |- nonlocal (local _) => fail 1
  |  |- nonlocal (prop _) => fail 1
  |  |- nonlocal (andp _ _) => fail 1
  |  |- nonlocal (sepcon _ _) => fail 1
  | |- _ => apply I
 end.

Lemma canon8: forall R1 R2 R3 PQR, do_canon ((R1 && R2) && R3) PQR = do_canon (R1 && (R2 && R3)) PQR.