Definition fin_stream {A: Type} (h: list A) : stream A.
exists (fun n => nth_error h n).
intros.
rewrite nth_error_None_iff in H0 |- *.
omega.
Defined.
Definition inf_stream {A: Type} (h: nat -> A) : stream A.
exists (fun n => Some (h n)).
intros.
congruence.
Defined.

Lemma fin_stream_n_stream {A: Type}: forall l: list A, is_n_stream (length l) (fin_stream l).
Definition empty_stream {A: Type}: stream A := fin_stream nil.