theorem curvatureK_real_increasing {ρ : ℝ} (hρ : ρ < 1) :
∀ J₁ J₂ : ℝ, 0 < J₁ → J₁ < J₂ →
curvatureK_real J₁ ρ < curvatureK_real J₂ ρ := by
intro J₁ J₂ hJ₁ hJ₁₂
simp only [curvatureK_real]
have h1ρ : 0 < 1 - ρ := by linarith
have hJ₂ : 0 < J₂ := by linarith
-- (1-ρ)(J₁-1)/J₁ < (1-ρ)(J₂-1)/J₂
-- ⟺ (J₁-1)/J₁ < (J₂-1)/J₂ (since 1-ρ > 0)
-- ⟺ (J₁-1)J₂ < (J₂-1)J₁ (cross multiply)
-- ⟺ J₁J₂ - J₂ < J₁J₂ - J₁
-- ⟺ J₁ < J₂ ✓
rw [div_lt_div_iff₀ hJ₁ hJ₂]
nlinarithPaper 1c, Section 2: K(J) as the Network Engine