theorem abs_iterMul_lt_one_iff {η lam : ℝ} (hlam : 0 < lam) (hη : 0 < η) :
|iterationMultiplier η lam| < 1 ↔ η < criticalStepSize lam := by
simp only [iterationMultiplier, criticalStepSize]
constructor
· intro h
rw [abs_lt] at h
rw [lt_div_iff₀ hlam]
linarith [h.1]
· intro h
rw [lt_div_iff₀ hlam] at h
rw [abs_lt]
constructor <;> nlinarith [mul_pos hη hlam]Discrete-Time Stability of CES Tâtonnement (Edge of Stability)