theorem factorShare_le_one {a : Fin J → ℝ} {ρ : ℝ} {x : Fin J → ℝ}
(ha : ∀ j, 0 ≤ a j) (hx : ∀ j, 0 ≤ x j)
(hden : 0 < ∑ i : Fin J, a i * (x i) ^ ρ) (j : Fin J) :
factorShare J a ρ x j ≤ 1 := by
have hsum := factorShare_sum_eq_one hden
have hnneg : ∀ k, 0 ≤ factorShare J a ρ x k :=
factorShare_nonneg ha hx (le_of_lt hden)
calc factorShare J a ρ x j
≤ ∑ k : Fin J, factorShare J a ρ x k :=
Finset.single_le_sum (fun k _ => hnneg k) (Finset.mem_univ j)
_ = 1 := hsumEconomics extensions for CES formalization: