Section Map.
Variables A B : Type.
Variable f : A -> B.
CoFixpoint map (s:Stream A) : Stream B := Cons (f (hd s)) (map (tl s)).

Lemma Str_nth_zipWith : forall n (a:Stream A) (b:Stream B), Str_nth n (zipWith a
b)= f (Str_nth n a) (Str_nth n b).