theorem perCapitaSurplus_eq_K_div_J {J ρ : ℝ} (_hJ : J ≠ 0) :
perCapitaSurplus J ρ = curvatureKReal J ρ / J := by
simp only [perCapitaSurplus, curvatureKReal]
have hJ2 : J ^ 2 = J * J := sq J
rw [hJ2, div_div]Paper 1c: Formal Calculus on K(J) and V(J)