Section Undup.
Variable X : eqType.
Implicit Types A B : list X.
Fixpoint undup A : list X :=
match A with
| nil => nil
| x::A' => if decision (x el A') then undup A' else  x :: undup A'
end.
End PowerRep.
(** Size induction from ICL *)

Lemma size_induction X (f : X -> nat) (p : X -> Prop) :
(forall x, (forall y, f y < f x -> p y) -> p x) ->
forall x, p x.