(** Some properties of [is_mill] and [dests_disjoint]. *)

Definition dests_disjoint (m1 m2: moves) : Prop :=
  list_disjoint (dests m1) (dests m2).

Lemma is_path_change_last_source: forall s s' d sigma, is_path (sigma ++ (s, d) :: nil) -> is_path (sigma ++ (s', d) :: nil).