---
title: "answer-span-why — Mova code model"
description: "Mova code model of world/src/span.rs: components with their labels, obernants and the model text."
url: "https://groupants.elamur.ai/free/en/mova/world/src/span.rs.groupant/extraction.groupant/why.groupant/"
---
Elamur: [Mova](https://md.mova.elamur.ai/free/en/) · [Dictionary](https://md.dictionary.elamur.ai/free/en/) · [Research](https://md.research.elamur.ai/free/en/) · **Groupants**

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# answer-span-why

The groupant beside world/src/span.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_fragment
- **status:** partial source bound model
- **source:** [`world/src/span.rs`](https://github.com/ElamurAI/mova-free/blob/main/world/src/span.rs)
- **source SHA-256:** `4d215ccd57884f41…`
- **covers:** Source scope beginning         Want::Why => {; selected node envelope, partial semantic coverage. (bytes 14990–18981)
- **part of:** [answer-span-extraction](https://md.groupants.elamur.ai/free/en/mova/world/src/span.rs.groupant/extraction.groupant/)
- **repository folder:** [`world/src/span.rs.groupant/extraction.groupant/why.groupant`](https://github.com/ElamurAI/mova-free/tree/main/world/src/span.rs.groupant/extraction.groupant/why.groupant)
- **repository commit:** `855da7bd4a7b`

> **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 source model | [forward](#forward) |
| **ast** | partial | `../../syntax.json` |
| **cost** | partial source model | [cost](#cost) |
| **descriptant** | partial source model | [epoch-memory](#epoch-memory) |
| **invariant** | partial source model | [invariant](#invariant) |
| **tests** | partial source model | [checks](#checks) |

## 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.

| id | type | label | where |
|---|---|---|---|
| `answer-span-why-behavior-complement` | behavior_complement | partial source model | [behavior-complement](#behavior-complement) |
| `answer-span-why-reverse-reconstruction` | reverse_reconstruction | partial source model | [reverse-reconstruction](#reverse-reconstruction) |
| `answer-span-why-chain-bound` | resource_boundary | partial source model | [chain-bound](#chain-bound) |
| `answer-span-why-reason-order` | priority_relation | partial source model | [reason-order](#reason-order) |

## Model text


Subject: world/src/span.rs, whole-file SHA-256 in manifest, baseline 4279da541. Domain: finite acyclic valid trees with consistent child lists, valid indices and terminating dependencies. Observation: a single call return, not semantic truth or reachability. Hold Tree, ans::lemmas and types::FEELING dependencies fixed; parser/model loading and external caller wiring are gaps. All entries are source-derived partial models. Exact-target definitions are not executable inverses; finite tests cannot establish universal correspondence.

### forward

Bounded ancestor scan, ordered structural reason patterns, then token fallbacks.

### invariant

WHY_MARK matches any mark word; When uses first mark word.

### cost

At most three chain scans, subtree/clean plus O(n) lexical scan.

### epoch-memory

2026-10-29: initial source-bound epoch. Preserve Num bypass, global Feel selection, early-return cleanup suppression, and verb_kids comment mismatch: code expands Xcomp only and checks no shared subject. No source changes or task-accuracy claim. Partial syntax has no semantic analysis or macro expansion.

### checks

Structural inventory checks hashes, references, types and node bounds only. Proposed oracle: enumerate small annotated acyclic trees and compare literal expected returns, including None and labels; mutate priority or echo inequality to obtain a red control. Any executed bounded evidence is recorded separately in root evidence.md; catalog examples remain proposed until recorded there.

### composition

Leaf scope shares immutable tree/question/helper contracts. Overlap with parent is not extra runtime work. Dependencies outside range remain opaque.

### behavior-complement

U=valid Want::Why calls x optional output; R=Why branch. Inner U minus R excludes Some when p absent and later-rule outputs after earlier matched return. No nearby Advcl is insufficient exclusion because other patterns/fallbacks exist.

Assumptions/evidence/status: common domain above; source-derived partial relation at bound revision. Approximation and held-fixed inputs are stated in the relation. Oracle: finite literal fixtures exercising both membership and nonmembership against the actual function, preserving ambiguous preimages. No linguistic correctness or universal proof inferred.

### reverse-reconstruction

advcl:because admits all chains with first qualifying outside-chain Advcl, stripped direct Mark/Cc then clean. words: because Y admits every earlier p, first qualifying post-p because/for/since with UPOS!=ADP and punctuation-bounded suffix. Deleted markers/context ambiguous.

Assumptions/evidence/status: common domain above; source-derived partial relation at bound revision. Approximation and held-fixed inputs are stated in the relation. Oracle: finite literal fixtures exercising both membership and nonmembership against the actual function, preserving ambiguous preimages. No linguistic correctness or universal proof inferred.

### chain-bound

p plus two head attempts through Xcomp/Ccomp/Obj/Conj/Advcl/Nsubj/Obl yields at most three chain nodes. No further structural ancestor scan; changing distant words may still affect lexical fallback.

Assumptions/evidence/status: common domain above; source-derived partial relation at bound revision. Approximation and held-fixed inputs are stated in the relation. Oracle: finite literal fixtures exercising both membership and nonmembership against the actual function, preserving ambiguous preimages. No linguistic correctness or universal proof inferred.

### reason-order

Per near-to-far node: WHY_MARK Advcl, later for/because Conj, later to-purpose, selected oblique cases, so-result head-minus-x, that-result head-minus-x. Then lexical X,so and because-Y. Ordered syntax heuristics are not causal entailment.

Assumptions/evidence/status: common domain above; source-derived partial relation at bound revision. Approximation and held-fixed inputs are stated in the relation. Oracle: finite literal fixtures exercising both membership and nonmembership against the actual function, preserving ambiguous preimages. No linguistic correctness or universal proof inferred.