proposition: Lemma AbsList_P1 : forall (l:list R) (x y:R), In y l -> In (Rabs (y - x) / 2) (AbsList l x).
proof: Proof. intros; induction l as [| r l Hrecl]. - elim H. - simpl; simpl in H; elim H; intro. + left; rewrite H0; reflexivity. + right; apply Hrecl; assumption. Qed.
imports: List Rbase Rfunctions