theorem npvOptimalBound_pos {η D₀ δ_gap : ℝ}
(hη : 0 < η) (hD : 0 < D₀) (hδ : 0 < δ_gap) :
0 < npvOptimalBound η D₀ δ_gap := by
simp only [npvOptimalBound]
apply div_pos hδ
apply mul_pos (by positivity : (0:ℝ) < 8 * η ^ 2)
linarith [div_pos hδ (show (0:ℝ) < 2 * η by linarith)]Growth and Dynamic Tax Revenue (Layer 4-5 of Macro Extension)