(** - Restriction of a sequence to its prefixes... not used anywhere any more *)

Definition restricted_seq :
  forall (S : Setoid) (N : Nat) (f : seq N S) (M : Nat) (leMN : M <= N),
  seq M S.

Lemma restricted_seq_preserves_distinct : forall (A : Setoid) (n m : Nat) (v : seq n A) (H : m <= n), distinct v -> distinct (restricted_seq v H).