def IsOddComposite (k : ℕ) : Prop :=
Odd k ∧ k > 1 ∧ ¬Nat.Prime k
lemma odd_prime_cui_and_composite_disjoint (k : ℕ) (h_odd : Odd k) (h_pos : 0 < k) :
¬ (IsOddPrimeCui k ∧ IsOddComposite k) := by
intro h
have h1 : k > 1 := h.2.2.1
have h2 : (k = 1 ∨ Nat.Prime k) := h.1.2
have h3 : ¬Nat.Prime k := h.2.2.2
rcases h2 with (h2 | h2)
· linarith
· contradiction
lemma odd_classify (k : ℕ) (h_odd : Odd k) (h_pos : 0 < k) :
IsOddPrimeCui k ∨ IsOddComposite k := by
by_cases h_p : Nat.Prime k
· left
exact ⟨h_odd, Or.inr h_p⟩
· right
have hk1 : k > 1 := by
by_contra h
have h' : k ≤ 1 := by linarith
have h0 : 0 < k := h_pos
interval_cases k <;> tauto
exact ⟨h_odd, hk1, h_p⟩
-- 四维坐标分量
def X (N : ℕ) : ℝ := (N : ℝ) / 2
def Y (N : ℕ) : ℝ := (C N : ℝ)
def Z (N : ℕ) : ℝ := (π N : ℝ)
def r (N : ℕ) : ℝ := (r2 N : ℝ)
-- 超平面方程
def HyperplaneEquation (N : ℕ) : Prop :=
X N - Y N - 2 * Z N + r N = 0
-- 恒等式等价于超平面方程
lemma identity_iff_hyperplane (N : ℕ) :
CuiKunIdentity N ↔ HyperplaneEquation N := by
simp [CuiKunIdentity, HyperplaneEquation, X, Y, Z, r]
<;> ring
-- 法向量 n=(1, -1, -2, 1)
def normal_vector : Fin 4 → ℝ := fun i =>
match i with
| 0 => 1
| 1 => -1
| 2 => -2
| 3 => 1
-- 主命题:偶数N≥4,满足崔坤恒等式 ⇒ r2(N) ≥ 2
theorem CuiKunMainConclusion :
∀ (N : ℕ), IsValidN N → CuiKunIdentity N → r2 N ≥ 2