theorem K_deficit_from_concentration (hJ : 0 < J) {ρ : ℝ}
{a : Fin J → ℝ} (_ha_sum : ∑ j : Fin J, a j = 1) :
curvatureK J ρ - generalCurvatureK J ρ a =
(1 - ρ) * (herfindahlIndex J a - 1 / ↑J) := by
simp only [curvatureK, generalCurvatureK, herfindahlIndex]
have hJne : (↑J : ℝ) ≠ 0 := Nat.cast_ne_zero.mpr (by omega)
field_simp
ring## Entry with General Weights