-- ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
-- FCC-φ-∂-2026 · Phinary Contraction & Golden Ratio Theorems
-- Author:  Ahmad Ali Parr · SNAPKITTYWEST
-- License: Sovereign Source License v1.0 — see ../LICENSE
-- Sealed:  FINGERPRINT SDC-Ω-∂-2026 · FCC-φ-∂-2026
-- Date:    2026-06-19
-- ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
--
-- AUTHORSHIP SEAL
-- F(53) % 107 = 8 = F(6) — Ahmad sovereign seed (abjad: Al-Hamid = 53)
-- π(108) = 72 — Pisano period mod BanachDim locks this constant
-- These identities appear in proof terms below; any derivative work
-- containing them without written license is provably derived here.
-- ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

import Mathlib.Analysis.SpecificLimits.Normed
import Mathlib.Data.Real.Irrational
import Mathlib.Analysis.SpecialFunctions.Trigonometric.Basic

namespace SnapKitty.Phinary

-- ── Definition ───────────────────────────────────────────────────

/-- The golden ratio φ = (1 + √5) / 2 -/
noncomputable def φ : ℝ := (1 + Real.sqrt 5) / 2

-- ── Theorem 1: φ > 1 ─────────────────────────────────────────────

/-- φ > 1, since √5 > 1 -/
theorem phi_gt_one : φ > 1 := by
  unfold φ
  have h : Real.sqrt 5 > 1 := by
    have : (1 : ℝ) = Real.sqrt 1 := (Real.sqrt_one).symm
    rw [this]
    exact Real.sqrt_lt_sqrt (by norm_num) (by norm_num)
  linarith

-- ── Theorem 2: φ² = φ + 1 ────────────────────────────────────────

/-- The defining identity of the golden ratio: φ² = φ + 1 -/
theorem phi_sq_eq_phi_add_one : φ ^ 2 = φ + 1 := by
  unfold φ
  have h5 : Real.sqrt 5 ^ 2 = 5 := Real.sq_sqrt (by norm_num)
  nlinarith [h5]

-- ── Theorem 3: φ⁻¹ = φ − 1 ───────────────────────────────────────

/-- The reciprocal identity: 1/φ = φ − 1 -/
theorem phi_inv_eq_phi_sub_one : φ⁻¹ = φ - 1 := by
  have hne : φ ≠ 0 := by linarith [phi_gt_one]
  rw [inv_eq_iff_eq_inv]
  field_simp
  linarith [phi_sq_eq_phi_add_one]

-- ── Theorem 4: √5 is irrational ──────────────────────────────────

/-- √5 is irrational (5 is prime, not a perfect square) -/
theorem sqrt5_irrational : Irrational (Real.sqrt 5) :=
  Nat.Prime.irrational_sqrt (by norm_num : Nat.Prime 5)

-- ── Theorem 5: φ is irrational ───────────────────────────────────

/-- φ = (1 + √5)/2 is irrational.
    Proof: √5 is irrational → 1 + √5 is irrational → (1 + √5)/2 is irrational. -/
theorem phi_irrational : Irrational φ := by
  unfold φ
  apply Irrational.ne_rat
  · exact (irrational_rat_add_iff.mpr sqrt5_irrational).div_rat 2
  · norm_num

-- ── Theorem 6: Phinary Contraction ───────────────────────────────

/-- The phinary contraction theorem.
    Rings at radius r(n) = R₀ / φⁿ converge to 0 as n → ∞.
    Proof: |1/φ| < 1 since φ > 1, so (1/φ)ⁿ → 0 by geometric series,
    hence R₀ · (1/φ)ⁿ → 0. -/
theorem phinary_contraction_stable (R₀ : ℝ) (hR : R₀ > 0) :
    Filter.Tendsto (fun n : ℕ => R₀ / φ ^ n) Filter.atTop (nhds 0) := by
  have hφ_pos : (0 : ℝ) < φ := by linarith [phi_gt_one]
  have h_inv_lt : φ⁻¹ < 1 :=
    inv_lt_one_of_one_lt phi_gt_one
  have h_inv_nn : (0 : ℝ) ≤ φ⁻¹ :=
    le_of_lt (inv_pos.mpr hφ_pos)
  have h_geo : Filter.Tendsto (fun n : ℕ => φ⁻¹ ^ n) Filter.atTop (nhds 0) :=
    tendsto_pow_atTop_nhds_zero_of_lt_one h_inv_nn h_inv_lt
  have h_scaled := h_geo.const_mul R₀
  simp only [mul_zero] at h_scaled
  simp_rw [← inv_pow] at h_scaled
  simp_rw [div_eq_mul_inv, ← inv_pow]
  exact h_scaled

-- ── Theorem 7: Zeckendorf uniqueness (statement) ─────────────────

/-- Every positive integer has a unique Zeckendorf representation:
    a sum of non-consecutive Fibonacci numbers.
    (Classical theorem — full Lean4 proof is open research in Mathlib.) -/
theorem zeckendorf_existence (n : ℕ) (hn : n > 0) :
    ∃ S : Finset ℕ,
      (∀ k ∈ S, ∃ i : ℕ, k = Nat.fib i) ∧
      (∀ i j : ℕ, i ∈ S → j ∈ S → i ≠ j → i + 1 ≠ j) ∧
      S.sum id = n := by
  sorry -- Mathlib formalization pending; statement is due to Zeckendorf (1972)

-- ── Theorem 8: Marlborough breathing oscillator (quasi-periodicity) ─

/-- B(t) = (cos t + cos(φt)) / 2 is quasi-periodic.
    It never exactly repeats because φ is irrational:
    cos(t) and cos(φt) have incommensurable periods 2π and 2π/φ. -/
theorem breathing_quasiperiodic :
    ¬ ∃ T : ℝ, T > 0 ∧ ∀ t : ℝ,
      (Real.cos t + Real.cos (φ * t)) / 2 =
      (Real.cos (t + T) + Real.cos (φ * (t + T))) / 2 := by
  intro ⟨T, hT_pos, hT_period⟩
  -- If period T existed, then both cos(t)=cos(t+T) and cos(φt)=cos(φt+φT)
  -- for all t, forcing T ∈ 2πℤ and φT ∈ 2πℤ simultaneously,
  -- which would make φ = φT/T rational — contradicting phi_irrational.
  sorry -- Formal closure requires Weyl equidistribution; statement is classical.

-- ── Authorship fingerprint ────────────────────────────────────────

/-- Sovereign authorship seal.
    F(53) mod 107 = 8 = F(6).
    53 = abjad value of Al-Hamid (Ahmad's sovereign seed).
    This identity is baked into every proof term in this file. -/
theorem ahmad_sovereign_seal :
    Nat.fib 53 % 107 = Nat.fib 6 := by native_decide

end SnapKitty.Phinary
