SilverSight/docs/fundamental_math/PURE_FORMULA_DERIVATION.md
allaun 1794299a6c chore(quality): native_decide migration, docs, and phi pipeline cleanup
Systematic native_decide → dec_trivial/rfl migration across all Lean modules
to comply with AGENTS.md rule 5 (no native_decide unless only option):
- CoreFormalism: BraidEigensolid, BraidField, ChentsovFinite, HachimojiBase,
  HachimojiBridging, HachimojiCodec, HachimojiLUT, HachimojiManifoldAxiom,
  Q16_16Numerics
- BindingSite: BindingSiteCodec, BindingSiteEntropy, BindingSiteHachimoji
- SilverSight: ProductSchema, ProductWireFormat, PolyFactorIdentity, Schema, WireFormat
- PVGS_DQ_Bridge: all three files (native_decide->dec_trivial)
- UniversalEncoding/ChiralitySpace

Additional changes:
- gemma4_mcp.py: upgraded to two-tier routing (local Gemma4 + FreeLLMAPI proxy)
- ChentsovFinite: added traceability map and Chentsov (1972) citation
- HachimojiBase: renamed Σ→Sig, Π→Pi to avoid non-ASCII issues
- Import path fixes for Mathlib 4.30.0-rc2 compatibility
- Doc updates: PURE_FORMULAS, SOS_CERTIFICATE, fundamental math derivations
- Build log: 2026-06-26 session findings
- BRKGLASS_NR_BRACKET_PROPOSAL: updated to REAL-DATA VALIDATED status
- New docs: FOUNDATIONAL_GUIDANCE, PURE_EQUATION_MAP, CHENTSOV_FINITE_MATH,
  BREAKGLASS_FUSION_REVIEW_SPEC, COLD_REVIEWER_FORMULA
- New python: phi pipeline (equation_dna_encoder, ast_parse, charclass,
  consistency, embed, output), nr_bracket_validation with receipt

Build: lake build SilverSightRRC — passes on all committed modules.
  Excluded: HachimojiN8Bridge, HachimojiCharClass (missing
  CoreFormalism.HachimojiManifoldAxiom olean — WIP)
2026-06-27 01:56:54 -05:00

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# PURE MATH FORMULA: Fisher Distance on Δ₇
## Zero English inside formulas. Each equality justified. Verifiable numerically.
---
> **Domain note:** All Fisher metric computations require \(p_i > 0\) for all \(i\). Raw byte frequencies produce \(p_i = 0\) for unseen classes. Apply **Laplace smoothing**: \(F(E)_i = (f_i + 1)/(|E| + 8)\) to ensure strict positivity. This keeps all computations in the open simplex \(\Delta_7\) and regularizes the Fisher metric near boundaries.
---
## THE CHAIN
**Given:** p, q ∈ Δ₇ (probability simplex, 8 dimensions)
**Step 0 — Chentsov's metric:**
g_p(u,v) = Σᵢ₌₁⁸ (uᵢ vᵢ / pᵢ)
**Justification:** Chentsov 1972, Amari 1985. Unique metric respecting sufficient statistics.
---
**Step 1 — The √p embedding:**
φ : Δ₇ → S⁷, φ(p) = (√p₁, √p₂, ..., √p₈)
**Lemma:** ‖φ(p)‖₂ = 1
‖φ(p)‖₂² = Σᵢ₌₁⁸ (√pᵢ)² = Σᵢ₌₁⁸ pᵢ = 1
**Justification:** p ∈ Δ₇ ⇒ Σpᵢ = 1 by definition.
---
**Step 2 — Pullback of round metric:**
(φ* g_{S⁷})_p(u,v) = ¼ · g_p(u,v)
**Proof sketch:**
Let c(t) be a curve in Δ₇, c(0) = p, ċ(0) = v.
γ(t) = φ(c(t)) = (√c₁(t), ..., √c₈(t))
γ̇ᵢ(0) = vᵢ / (2√pᵢ)
Round metric on S⁷:
⟨γ̇, γ̇⟩_{S⁷} = Σᵢ γ̇ᵢ² = Σᵢ vᵢ² / (4pᵢ) = ¼ · Σᵢ vᵢ²/pᵢ = ¼ · g_p(v,v)
**Justification:** Chain rule + direct computation.
---
**Step 3 — Geodesics are great circles:**
S⁷ has round metric ⇒ geodesics are great circles.
Great-circle distance:
d_{S⁷}(a,b) = arccos(⟨a,b⟩)
**Justification:** Standard Riemannian geometry of the sphere.
---
**Step 4 — Inner product on S⁷:**
⟨φ(p), φ(q)⟩ = Σᵢ₌₁⁸ √(pᵢ qᵢ)
**Justification:** Definition of φ + Euclidean inner product.
---
**Step 5 — Fisher distance (THE FORMULA):**
d_F(p,q) = 2 · d_{S⁷}(φ(p), φ(q))
= 2 · arccos(⟨φ(p), φ(q)⟩)
= 2 · arccos( Σᵢ₌₁⁸ √(pᵢ qᵢ) )
**Justification:** Steps 2+3+4 combined. The factor 2 comes from Step 2 (g = 4·φ*g_{S⁷}).
---
## THE CLOSED-FORM RESULT
```
┌─────────────────────────────────────────────────────┐
│ │
│ d_F(p,q) = 2 · arccos( Σᵢ₌₁ⁿ √(pᵢ qᵢ) ) │
│ │
│ Domain: p, q ∈ Δₙ (any dimension n ≥ 2) │
│ Range: [0, π] │
│ Equality: d_F(p,q) = 0 ⟺ p = q │
│ Max: d_F(p,q) = π when p, q are antipodal │
│ (e.g., p = (1,0,...,0), q = (0,1,0,...,0)) │
│ │
└─────────────────────────────────────────────────────┘
```
---
## VERIFICATION INSTANCE (n=8)
**Inputs:**
p = (0.3, 0.1, 0.15, 0.05, 0.2, 0.08, 0.07, 0.05)
q = (0.2, 0.2, 0.1, 0.1, 0.15, 0.1, 0.1, 0.05)
**Step A — Compute √(pᵢqᵢ):**
√(0.3×0.2) = 0.24494897
√(0.1×0.2) = 0.14142136
√(0.15×0.1) = 0.12247449
√(0.05×0.1) = 0.07071068
√(0.2×0.15) = 0.17320508
√(0.08×0.1) = 0.08944272
√(0.07×0.1) = 0.08366600
√(0.05×0.05) = 0.05000000
**Step B — Sum:**
S = 0.97586930
**Step C — Arccos:**
arccos(0.97586930) = 0.22012896
**Step D — Multiply by 2:**
d_F(p,q) = 2 × 0.22012896 = 0.44025792
**OUTPUT: d_F(p,q) ≈ 0.440258**
---
## PROPERTIES (all verifiable)
**Symmetry:**
d_F(p,q) = 2·arccos(Σ√(pᵢqᵢ)) = 2·arccos(Σ√(qᵢpᵢ)) = d_F(q,p) ✓
**Identity:**
d_F(p,p) = 2·arccos(Σ√(pᵢpᵢ)) = 2·arccos(Σpᵢ) = 2·arccos(1) = 0 ✓
**Triangle inequality:**
d_F(p,q) ≤ d_F(p,r) + d_F(r,q) for all p,q,r ∈ Δ₇
Proof: Great-circle distance on S⁷ satisfies triangle inequality.
Pullback by isometry preserves triangle inequality. ✓
**Bound:**
0 ≤ d_F(p,q) ≤ π
Proof: arccos: [-1,1] → [0,π]. The argument Σ√(pᵢqᵢ) ∈ [0,1]
by Cauchy-Schwarz: (Σ√(pᵢqᵢ))² ≤ (Σpᵢ)(Σqᵢ) = 1. ✓
---
## WHY THIS IS THE RIGHT FORMULA
1. **Chentsov's theorem** says: any metric respecting sufficient statistics
MUST be the Fisher metric (up to constant).
2. **The √p embedding** maps Δ₇ → S⁷ isometrically (up to factor 4).
3. **Geodesics on S⁷** are great circles with known distance formula.
4. **Pulling back** gives the Fisher distance formula above.
There is no choice in this formula. It is forced by the geometry of the
probability simplex combined with Chentsov's uniqueness result.