theorem saddle_point_substitutes
(hJ : 2 ≤ J) {ρ : ℝ} (hρ : 1 < ρ)
{c : ℝ} (hc : 0 < c)
(v : Fin J → ℝ) (hv : orthToOne J v)
(hv_ne : ∃ j, v j ≠ 0) :
0 < cesHessianQF J ρ c v := by
rw [cesHessianQF_on_perp (by omega) ρ c hc v hv]
apply mul_pos
· simp only [cesEigenvaluePerp]
apply div_pos (by linarith)
exact mul_pos (by exact_mod_cast (by omega : 0 < J)) hc
· exact Finset.sum_pos'
(fun j _ => sq_nonneg (v j))
(by obtain ⟨j₀, hj₀⟩ := hv_ne
exact ⟨j₀, Finset.mem_univ _, by positivity⟩)Multi-Agent CES Game Theory (Gap #14)