---
title: "mova-nightingale-delta — Mova code model"
description: "Mova code model of tools/nightingale/src/delta.rs: components with their labels, obernants and the model text."
url: "https://groupants.elamur.ai/free/en/mova/tools/nightingale/src/delta.rs.groupant/"
---
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# mova-nightingale-delta

The groupant beside tools/nightingale/src/delta.rs in the Mova repository: what the code computes, what it never does, how to go back from its outputs, its invariants, cost and checks.

## Facts

- **kind:** groupant
- **status:** partial source bound model
- **source:** [`tools/nightingale/src/delta.rs`](https://github.com/ElamurAI/mova-free/blob/main/tools/nightingale/src/delta.rs)
- **repository folder:** [`tools/nightingale/src/delta.rs.groupant`](https://github.com/ElamurAI/mova-free/tree/main/tools/nightingale/src/delta.rs.groupant)

> **Implementation material.** A Mova code model describes this code at one source revision: partial models, finite checks and their stated scope. It is not a reviewed general exposition, and its labels are shown as written, never raised.

## Components

| component | label | where |
|---|---|---|
| **Approximant** | partial | [Forward approximant](#forward-approximant) |
| **Ast** | partial | `syntax.json` |
| **Composition** | partial | [Composition](#composition) |
| **Cost** | partial | [Cost](#cost) |
| **Descriptant** | present | [Descriptant](#descriptant) |
| **Invariant** | partial | [Invariant](#invariant) |
| **Tests** | finite evidence | [Tests](#tests) |

## Obernants

The typed relations around the forward model: the behaviour complement (what the code never does), the reverse reconstruction (every input compatible with an output) and specialised views.

| relation | type | label | where |
|---|---|---|---|
| Behavior complement | behavior complement | partial source derived model | [Behavior complement](#behavior-complement) |
| Reverse reconstruction | reverse reconstruction | partial source derived model | [Reverse reconstruction](#reverse-reconstruction) |

## Model text


### Descriptant

Varieties as deltas over the standard: per-facet log ratios for forms and bigrams, kept by evidence, size and Dunning's G2, written beside the model and composed log-linearly by a label's facets. Source: `tools/nightingale/src/delta.rs`.

### Forward approximant

learn: for each facet with text on both sides and each f/b record, delta = log2((cF+1/2)/NF) - log2((cR+1/2)/NR), kept if cF+cR >= 5, |delta| >= 1 bit, G2 >= 10.83, top 200 000 by G2; shift(label) = sum of the facets' deltas, unknown facets reported.

### Invariant

A facet without text on both sides learns nothing; deltas are read only for their model's lineage.

### Cost

O(facets x records) at a handoff (seconds on the probes).

### Composition

Parent: nightingale.

### Behavior complement

Never changes the standard's counts. Evidence status: source-derived model with finite checks, not a proof.

### Reverse reconstruction

deltas.tsv keeps each delta's counts on both sides, so the estimate can be recomputed.

### Tests

#### Checks

tests/model.rs varieties test; random-split control learns 0 deltas.
These are finite fixtures and measurements; not a proof.

## History


#### 2026-11-06 · document

##### Epoch 2026-11-06

First model, written with the source (the Nightingale: one per language under the Eel; a standard naturalness model with variety deltas).

## Provenance

- **source SHA-256:** `b3d9cce728ba2dba…`
- **repository commit:** `2e25d7bfae9a`