theorem ngm_char_poly_two_level (k10 k21 : ℝ) (hk10 : 0 < k10) (hk21 : 0 < k21) :
-- The product of the two NGM entries gives the cycle product
-- The spectral radius squared equals the cycle product
Real.sqrt (k10 * k21) ^ 2 = k10 * k21 := by
rw [sq_sqrt (mul_nonneg (le_of_lt hk10) (le_of_lt hk21))]Theorems 5-6, Proposition 3: Next-Generation Matrix and Activation Threshold