(** ** SF_size *)
Definition SF_size (s : SF_seq) := size (SF_t s).

(* Specifications: *)
Lemma SF_size_cons (h : R*T) (s : SF_seq) : SF_size (SF_cons h s) = S (SF_size s).
Lemma SF_size_rcons (s : SF_seq) (t : R*T) : SF_size (SF_rcons s t) = S (SF_size s).
Lemma SF_size_lx (s : SF_seq) : size (SF_lx s) = S (SF_size s).
Lemma SF_size_ly (s : SF_seq) : size (SF_ly s) = SF_size s.
(** ** SF_rev *)
Lemma SF_rev_0 (s : SF_seq) :
size (rev (SF_lx s)) = S (size (rev (SF_ly s))).