# Terminology

Short, so that it is actually read. Where a term already has a standard meaning
in the literature, we use the standard meaning and say so rather than inventing
a synonym.

## Economic units (inherited from Nodus v1)

| Term | Meaning |
|---|---|
| **CU** | Compute Unit. A quantity of computational work. CU-v0 = 100 tokens of a fixed reference workload (`../nodus/shared/cu.py`). |
| **CC** | Compute Credit. The transferable accounting unit, integer micro-credits. |
| **CU-v0** | The current, workload-anchored definition. Its weakness: `model_weight` is DECLARED, and token counts are provider-reported. |
| **Verified CU (vCU)** | *New here.* A CU for which evidence at a stated level supports a stated claim set. `vCU` is always qualified: "vCU(A, L3, 2^-40)" means one CU whose correctness is supported by an L3 mechanism with soundness error 2^-40. An unqualified "verified CU" is meaningless. |
| **Cost of verified CU** | `cost(CU) + cost(evidence)`. The metric the whole programme optimises. |

## Verification vocabulary

| Term | Meaning |
|---|---|
| **Claim O/A/B/C/D/E** | Origin / Correctness / Execution / Work / Physical resource / Useful computation. Defined in `verification-taxonomy.md`. |
| **L0–L6** | Evidence strength ladder, from bare assertion to unconditional. |
| **Proof** | Reserved for L5/L6. Never used for a random audit. |
| **Check** | An L2/L3 mechanism. Has a soundness error, which must be quoted. |
| **Attestation** | A signed statement by a hardware root of trust (L4). Not a proof. |
| **Receipt** | An authenticated summary of a claimed execution (L1). What v1 has. |
| **Soundness error** | Probability that a cheating prover is accepted, per check. |
| **`R`** | `cost of evidence / cost of native computation`. The headline metric. |
| **`R_prove` / `R_verify`** | The provider-side and verifier-side components of `R`. `R_verify` is the one that decides whether a scheme beats re-execution. |
| **Re-execution baseline** | Running the job again. `R_verify = 1` by definition. Every mechanism is quoted against it. |
| **Model binding** | Cryptographically tying evidence to *specific weights*, usually via a commitment. Without it, model substitution is undetectable. |
| **Freshness binding** | Tying evidence to *this* execution occasion, usually via an unpredictable value chosen after job assignment. Without it, cached results and precomputation are undetectable. |

## Evidence labels

Inherited from `../nodus/PAPER_BRIEF.md` and used identically here:

- **MEASURED** — we ran it and recorded it.
- **DERIVED** — computed from measured values; the derivation is shown.
- **DECLARED** — a human chose the number. Always flagged.
- **SPECULATIVE** — a plausible idea with no evidence.
- **UNKNOWN** — we looked and do not know. Preferred over a guess.