Section prodl.
Fixpoint prodl (l : list nat) : nat :=
match l with
| nil => 1
| n :: l' => n * prodl l'
end.
End prodl.
Definition clos_refl {A : Type} (R : A -> A -> Prop) (x y : A) : Prop :=
R x y \/ x = y.

Lemma Forall_In_l (A : Type) (P : A -> Prop) x xs:
Forall P xs -> In x xs -> P x.