theorem cross_level_amplification {N : ℕ} (k : Fin N → ℝ)
(hk : ∀ n, 0 < k n)
(hprod : 1 < ∏ n : Fin N, k n) :
∃ n, 1 < k n := by
by_contra h
push_neg at h
have hle : ∏ n : Fin N, k n ≤ 1 := by
calc ∏ n : Fin N, k n
≤ ∏ _n : Fin N, (1 : ℝ) := by
exact Finset.prod_le_prod (fun n _ => le_of_lt (hk n)) (fun n _ => h n)
_ = 1 := by simp
linarithTheorems 5-6, Proposition 3: Next-Generation Matrix and Activation Threshold