Variable elt':Type.
(** * [map] and [mapi] *)
Fixpoint map (f:elt -> elt') (m:t elt) : t elt' :=
match m with
| nil => nil
| (k,e)::m' => (k,f e) :: map f m'
end.
Fixpoint mapi (f: key -> elt -> elt') (m:t elt) : t elt' :=
match m with
| nil => nil
| (k,e)::m' => (k,f k e) :: mapi f m'
end.
End Elt.
Section Elt2.
(* A new section is necessary for previous definitions to work with different [elt], especially [MapsTo]... *)
Variable elt elt' : Type.
(** Specification of [map] *)

Lemma map_2 : forall (m:t elt)(x:key)(f:elt->elt'),
In x (map f m) -> In x m.