theorem variance_decay_monotone (S₀ : ℝ) (hS : 0 < S₀) (r : ℝ)
(hr0 : 0 < r) (hr1 : r < 1) (n : ℕ) :
S₀ * r ^ (n + 1) < S₀ * r ^ n := by
have : r ^ (n + 1) < r ^ n := by
rw [pow_succ']
exact mul_lt_of_lt_one_left (pow_pos hr0 n) hr1
exact mul_lt_mul_of_pos_left this hSResults 86-92: Endogenous Variance Dynamics