theorem dtcPremium_threshold_sigma_2 {α K L : ℝ}
(_hK : 0 < K) (_hL : 0 < L) :
(α / (1 - α)) * (K / L) ^ ((2 : ℝ) - 2) = α / (1 - α) := by
rw [show (2 : ℝ) - 2 = 0 from by ring]
simp [rpow_zero]Directed Technical Change Extension (Acemoglu 2002)