Definition no_rt (c : Config) :=
  forall s1 : Site, In s1 LS -> s1 <> owner -> rt c s1 = false.

Lemma sigma_f_null : forall (E : Set) (f : E -> Z) (l : list E), (forall x_ : E, f x_ = 0%Z) -> sigma E l f = 0%Z.