Definition SF_cons (h : R*T) (s : SF_seq) :=
  mkSF_seq (fst h) ((SF_h s,snd h)::(SF_t s)).Definition SF_rcons (s : SF_seq) (t : R*T) :=
  mkSF_seq (SF_h s) (rcons (SF_t s) t).

Lemma SF_cons_ind (P : SF_seq -> Type) : (forall x0 : R, P (SF_nil x0)) -> (forall h s, P s -> P (SF_cons h s)) -> (forall s, P s).