theorem ces_period_two_at_critical {J : ℕ} (hJ : 0 < J) {ρ : ℝ} (hρ : ρ < 1)
{c : ℝ} (hc : 0 < c) :
iterationMultiplier (cesCriticalStep J ρ c) (abs (cesEigenvaluePerp J ρ c)) = -1 :=
iterMul_eq_neg_one_at_critical (cesEigenvaluePerp_abs_pos hJ hρ hc)Discrete-Time Stability of CES Tâtonnement (Edge of Stability)