(** [Loc.norepet ll] holds if the locations in list [ll] are pairwise different. *)
Inductive norepet : list loc -> Prop :=
| norepet_nil:
norepet nil
| norepet_cons:
forall hd tl, notin hd tl -> norepet tl -> norepet (hd :: tl).

Lemma norepet_dec (ll: list loc) : {norepet ll} + {~norepet ll}.