# AVM ISA Value Derivation

Every AVM constant traces back to one of the **4 fundamental equations**
(`UnifiedCovariant.lean:12-24`). No parameter tuning. No magic numbers.

---

## The 4 Fundamental Equations

| ID | Equation | Domain | Source |
|----|----------|--------|--------|
| **I₁** | φ² − φ − 1 = 0 | Golden ratio braid scaling | Braid crossing operator |
| **I₂** | σ − τ = 17/1792 > 0 | Spectral gap positivity | Cartan connection weights |
| **I₃** | F₇ = 13, F₈ = 21 | Fibonacci Temperley-Lieb dimensions | TL quotient |
| **I₄** | 2^a + 2^b = 2^c + 2^d ⇒ {a,b} = {c,d} | Sidon address uniqueness | Binary expansion |

### Constants derived from I₂

```
σ = 9984/65536 = 39/256           spectral radius (Cartan diagonal weight)
τ = 1/7                           spectral threshold (chaotic floor)
D = lcm(7, 256) = 1792            exact integer denominator
σ·D = 39 × 7 = 273                integer LHS
τ·D = 1 × 256 = 256               integer RHS
gap = 273 − 256 = 17              signed integer difference
σ − τ = 17/1792                   exact rational gap
```

### Domain provenance

| Constant | Origin | Equation |
|----------|--------|----------|
| 7 | Sidon doublings (2→128, 7 steps) | I₂, I₄ |
| 256 = 2⁸ | 8-strand braid, 8-bit precision | I₄ |
| 1792 = 7 × 256 | LCM of denominators | I₂ |
| 39 = (7+1)(7+1)/2 − 1 | Cartan C₂ weight | I₂ |
| 9984 = 39 × 256 | σ in Q16_16 units | I₂ |

---

## Derivation: AVM Types

| Type | Derivation | Equation |
|------|-----------|----------|
| `Q16_16` | Crossing weights (39/256, 1/7), spectral gap (17/1792) require 16 integer + 16 fraction bits | I₂ |
| `Q0_16` | Simplex probabilities (p ∈ [0,1]) for Fisher metric on Δ₇ | I₁ (Chentsov forces Fisher) |
| `Bool` | Comparison results for eigensolid detection, Sidon uniqueness | I₄ |

**Why not more types?** The 3-type universe is the minimum needed to represent:
- The C crossing matrix (Q16_16 entries)
- Tangent vectors on Δ₇ (Q0_16 simplex)
- Sidon comparisons and gap detection (Bool)

No UInt8, Int32, or Float types — they are not needed for any equation I₁–I₄.

---

## Derivation: 11 Primitives

### Q16_16 arithmetic (6 primitives from I₂ + I₄)

| Primitive | Needed for | Equation |
|-----------|-----------|----------|
| `addSatQ16` | Accumulate crossing weights; `C[i,k]·X[k]` sum | I₂ |
| `subSatQ16` | Receipt normalization; `e_i − e_j` tangent vectors | I₂ |
| `mulSatQ16` | Crossing matrix × state vector: `(C·s)_i = Σ C[i,j]·s[j]` | I₂, I₄ |
| `divSatQ16` | Receipt dimension scaling; `× 65536` in div | I₂ |
| `ltQ16` | Spectral gap check: `σ − τ > 0`, eigensolid detection | I₂ |
| `eqQ16` | Fixed-point check: `crossStep(s) = s` | I₂ |

All Q16_16 operations are **saturating** (not wrapping). Saturation ensures
`crossStep(s) = s` has a unique fixed point — wrapping would create aliases.

### Q0_16 arithmetic (2 primitives from I₁ + Chentsov)

| Primitive | Needed for | Equation |
|-----------|-----------|----------|
| `addSatQ0` | Probability accumulation on Δ₇ | I₁ |
| `subSatQ0` | Tangent vector difference; Fisher metric | I₁ |

### Boolean logic (3 primitives from I₄)

| Primitive | Needed for | Equation |
|-----------|-----------|----------|
| `and` | Gap condition: `gap(s) ∧ gap(e)` | I₄ |
| `or` | Control flow; type checking | I₄ |
| `not` | Complement; cross-block detection | I₄ |

### Why these 11 and no more?

- **No `sqrt`**: The spectral gap is rational (17/1792). No irrational spectral
  computation is required for the PIST classification gate.
- **No `abs`**: Crossing weights are non-negative; Sidon uniqueness (I₄) is
  a boolean condition, not a magnitude.
- **No `sin`/`cos`**: Phase accumulation is linear (crossing sum, not
  trigonometric). Trigonometric functions are pulled in at the Hopf fibration
  layer (HopfFibration.lean), not the AVM ISA.
- **No `fma`**: `mulSatQ16` + `addSatQ16` is sufficient — the crossing matrix
  has max 2 non-zero entries per row (block-diagonal from I₄).

---

## Derivation: 10 Instructions

| Instruction | Needed for | Derivation |
|-------------|-----------|------------|
| `push` | Stack-based evaluation model | Minimal formal semantics |
| `pop` | Discard computed value | Stack management |
| `dup` | Duplicate for paired operations | Sidon pair comparison (I₄) |
| `swap` | Reorder operands | Binary operation order |
| `load` | Read local variables | Crossing matrix row cache |
| `store` | Write local variables | Accumulator update |
| `jump` | Loop for braid steps (k iterations) | Eigensolid convergence loop |
| `jumpIf` | Conditional branch on gap condition | `σ − τ > 0` check (I₂) |
| `prim` | Dispatch arithmetic primitives | Finite closed-world dispatch |
| `halt` | Termination | Total execution guarantee |

**Why stack-based?** Stack semantics have the simplest formal model:
- `step(program, state)` is a structural induction on the instruction list
- No register allocation needed in the formal proof
- Trivially cross-language (every language has lists)
- Fuel argument gives a total run function

**Why 10?** This is the minimum usable set:
- 4 stack ops (push, pop, dup, swap)
- 2 memory ops (load, store)
- 2 control flow ops (jump, jumpIf)
- 1 primitive dispatch (prim)
- 1 termination (halt)

No `call`/`ret`: the braid loop is a straight-line pipeline (no dynamic
dispatch). Jump + locals is sufficient for all finite-state programs
needed by I₁–I₄.

---

## Derivation: Scaling Constants

| Constant | Value | Derivation | Equation |
|----------|-------|-----------|----------|
| `65536` | 2¹⁶ | Standard Q16_16 fraction bits; enough to resolve 17/1792 ≈ 0.0095 to 3.5 bits of precision | I₂ |
| `2147483647` | INT32_MAX | Symmetric upper bound for saturated arithmetic; guarantees `neg(neg(x)) = x` | I₂ (receipt invertibility) |
| `−2147483647` | −(INT32_MAX) | Symmetric lower bound; INT32_MIN (−2147483648) excluded because `neg(INT32_MIN) = INT32_MIN` | I₂ |
| `32767` | INT16_MAX / 2 | Q0_16 symmetric bound for simplex probabilities | I₁ |
| `−32767` | −32767 | Symmetric; INT16_MIN excluded for same negation-involution reason | I₁ |
| `1024` | stack depth | ~12 KB max (1024 × ~12 bytes), fits L1 cache | I₂ (k ≤ 1024 for braid loops) |
| `9984` | 39 × 256 | `σ` in Q16_16 raw units: `9984/65536 = 39/256` | I₂ |
| `273` | 39 × 7 | `C_int[i,i]` = 1792 × σ in the integer bypass | I₂ |
| `256` | 2⁸ | `C_int[i,j]` = 1792 × τ for paired strands | I₂, I₄ |

---

## Derivation: Crossing Matrix Structure

From I₂ + I₄, the crossing weight matrix C has a fixed block-diagonal structure:

```
C[i,j] = 
  σ = 39/256          if i = j             (I₂: diagonal)
  τ = 1/7             if i/2 = j/2, i ≠ j  (I₂: same-block off-diagonal)
  0                   if i/2 ≠ j/2          (I₄: cross-block zero)
```

This is not an approximation — it is forced by the Sidon pair structure (I₄):
strand pairs (0,1), (2,3), (4,5), (6,7) are the only interacting pairs.
All cross-block entries are structurally zero.

The 4 disjoint 2×2 blocks mean every matrix-vector multiply requires at most
2 multiplications and 1 addition per row — hence the primitive set needs only
`addSatQ16`, `mulSatQ16`, and no `fma` or vector primitives.

---

## Derivation: Symmetric Clamping (Negation Involution)

Receipt invertibility (`decode(encode(s)) = s`) requires every operation to
have a well-defined inverse. For negation, this means:

```
∀ x ∈ AVM.values: neg(neg(x)) = x
```

Standard INT32_MIN (−2147483648) fails: `neg(INT32_MIN) = INT32_MIN` (wraps).

Fix: clamp to [−2147483647, 2147483647] instead of INT32 full range.
Now `neg(neg(x)) = x` for every representable value.

This is not a cosmetic choice — it is required by **I₂** (receipt invertibility
for the crossing matrix). Without symmetric clamping, receipt decoding would
have a branching condition for the INT32_MIN case, which would break the
bijection proof.

---

## Derivation: Fuel and Totality

Every AVM program must terminate. The `run` function takes a `Fuel` parameter:

```
run : Fuel → Program → State → Outcome State
```

The braid loop converges in at most k ≤ 1024 steps (empirically from the
spectral gap: `σ − τ = 17/1792 ≈ 0.95% contraction per step`, so
`(1775/1792)^k ≤ ε` gives k ≤ 1024). The fuel bound of 1024 comes from this
contraction rate.

---

## Summary: What Is Not Tunable

| AVM feature | Tuning? | Why |
|-------------|---------|-----|
| 3 types | No | Minimum to represent I₁–I₄ |
| 11 primitives | No | Minimum closed-world for C matrix + Bool |
| 10 instructions | No | Minimum for stack-based execution |
| 65536 scale | No | Standard Q16_16; 2¹⁶ fraction bits |
| 1792 denominator | No | lcm(7, 256) from I₂ |
| 17/1792 gap | No | σ − τ = 39/256 − 1/7, exact rational |
| Symmetric clamping | No | Required by negation involution |
| Stack depth 1024 | No | Bounded by contraction rate |
| Block-diagonal C matrix | No | Forced by Sidon pair structure (I₄) |
| Saturating arithmetic | No | Required for unique fixed point |
| No CALL/RET | No | No dynamic dispatch in braid pipeline |
| No Float | No | Float breaks associativity, breaks invertibility |

Every AVM value and design decision traces back to one of the 4 equations.
If an AVM value cannot be linked to I₁, I₂, I₃, or I₄, it is a bug.

---

## References

| File | Content |
|------|---------|
| `formal/SilverSight/PIST/UnifiedCovariant.lean` | 4 fundamental equations (I₁–I₄) |
| `formal/SilverSight/PIST/CartanConnection.lean` | Integer bypass using D = 1792 |
| `formal/SilverSight/PIST/YangBaxter.lean` | 2×2 Sidon crossing block B |
| `formal/SilverSight/AVMIsa/Instr.lean` | 11 primitives, 10 instructions |
| `formal/SilverSight/AVMIsa/Step.lean` | Step semantics, symmetric clamping |
| `formal/SilverSight/AVMIsa/Types.lean` | 3-type universe |
| `docs/avm_isa_audit.md` | Wolfram Alpha arithmetic audit |
| `docs/reviews/CARTAN_CONNECTION_FORMULA.md` | Cartan connection formula derivation |
| `docs/reviews/SIDON_ORTHOGONALITY_BYPASS_FORMULA.md` | Spectral gap derivation |