(* The AGM, unscaled but without the nth root. *)

Lemma lerif_AGM (I : finType) (A : pred I) (E : I -> F) :
let n := #|A| in let mu := (\sum_(i in A) E i) / n%:R in
{in A, forall i, 0 <= E i} ->
\prod_(i in A) E i <= mu ^+ n
?= iff [forall i in A, forall j in A, E i == E j].