theorem piketty_r_gt_g {r g s_K s δ : ℝ}
(hδ : 0 < δ) (hs : 0 < s)
(h_solow : s_K = r * s / δ) :
r > g ↔ s_K > g * s / δ := by
subst h_solow
constructor
· intro h
exact div_lt_div_of_pos_right (mul_lt_mul_of_pos_right h hs) hδ
· intro h
rw [gt_iff_lt] at h ⊢
by_contra h_neg
push_neg at h_neg
have : r * s ≤ g * s := mul_le_mul_of_nonneg_right h_neg (le_of_lt hs)
have : r * s / δ ≤ g * s / δ := div_le_div_of_nonneg_right this (le_of_lt hδ)
linarithCES Inequality Decomposition