theorem crossing_at_Qstar {p₀ p_d τ β : ℝ}
(hp₀ : 0 < p₀) (hpdτ : 0 < p_d + τ) (hβ : β ≠ 0) :
cleanEnergyCost p₀ β (crossingProduction p₀ p_d τ β) =
effectiveDirtyCost p_d τ := by
simp only [cleanEnergyCost, crossingProduction, effectiveDirtyCost]
-- Goal: p₀ * ((p₀ / (p_d + τ)) ^ (1 / β)) ^ (-β) = p_d + τ
have hbase : (0 : ℝ) ≤ p₀ / (p_d + τ) := le_of_lt (div_pos hp₀ hpdτ)
-- Combine exponents: (x^{1/β})^{-β} = x^{(1/β)·(-β)} = x^{-1}
rw [← rpow_mul hbase]
have hexp : (1 / β * (-β) : ℝ) = -1 := by field_simp
rw [hexp, rpow_neg_one (p₀ / (p_d + τ)), inv_div]
-- p₀ * ((p_d + τ) / p₀) = p_d + τ
field_simpGreen Energy Transition Extension