theorem Keff_linear_near_critical {J : ℕ} {ρ T Tstar : ℝ}
(hT : 0 < Tstar) (hTlt : T < Tstar) :
effectiveCurvatureKeff J ρ T Tstar =
curvatureK J ρ * (1 - T / Tstar) := by
unfold effectiveCurvatureKeff
have h : 0 < 1 - T / Tstar := by rw [sub_pos, div_lt_one hT]; exact hTlt
rw [max_eq_right h.le]Renormalization Group for CES: