theorem acr_gains_gt_one {lam ρ : ℝ}
(hlam : 0 < lam) (hlam1 : lam < 1) (hρ : 0 < ρ) (hρ1 : ρ < 1) :
1 < acrGainsFromTrade lam ρ := by
simp only [acrGainsFromTrade]
have hexp_neg : -(1 / ρ - 1) < 0 := by
rw [neg_lt_zero, sub_pos, lt_div_iff₀ hρ, one_mul]
exact hρ1
calc (1 : ℝ) = lam ^ (0 : ℝ) := (rpow_zero lam).symm
_ < lam ^ (-(1 / ρ - 1)) := by
exact rpow_lt_rpow_of_exponent_gt hlam hlam1 hexp_negEconomics extensions for CES formalization: