theorem welfare_loss_decrease_rate {N : ℕ}
(ℓ : Fin N → ℝ) (hℓ : ∀ n, 0 < ℓ n) (grad : Fin N → ℝ)
(hgrad : ∃ n, grad n ≠ 0) :
0 < ∑ n : Fin N, ℓ n * (grad n) ^ 2 := by
obtain ⟨n₀, hn₀⟩ := hgrad
apply Finset.sum_pos'
· intro n _; exact mul_nonneg (le_of_lt (hℓ n)) (sq_nonneg _)
· exact ⟨n₀, Finset.mem_univ _, mul_pos (hℓ n₀) (by positivity)⟩Results 1-7: Relaxation on the CES Potential Landscape