# ADR-0136.S.3 — Compound Initial-Mutation Extractor

**Status:** Accepted — *regex patterns scheduled for removal under [ADR-0164](./ADR-0164-incremental-comprehension-reader.md) Phase 3; closed-set vocabulary preserved as lexicon seed*
**Parent:** ADR-0136 (Statement Layer Corridor) — see [ADR-0136 §Amendment 2026-05-26](./ADR-0136-statement-layer-corridor.md)
**Date:** 2026-05-23

## Context

The v2 refusal taxonomy (ADR-0136.S.2) identified 6 cases with `compound_statement`
as primary barrier. These cases contain two operations fused into a single sentence.
S.3 targets exactly one canonical shape — the initial-mutation form:

```
<Entity> had <N> <unit> [initially], but [then] <verb> <M>.
```

This is the simplest compound shape: a single derived `InitialPossession(entity, N ± M, unit)`
candidate, same topology as `_CONJ_EMBEDDED_RE`'s SUM-emission pattern. Other compound
shapes (fraction-of-remainder, percentage-of, age-multiplier, verb-conjunction) are
structurally different and out of scope.

## Decision

### One shape, not "all of compound_statement"

The 6 compound_statement cases represent at least 5 distinct structural shapes. S.3
ships one extractor for the initial-mutation form only. Bundling multiple shapes
would conflate distinct parser risks and violate the one-shape-per-PR discipline.

### Closed verb sets

Past-tense only (the "had N, but then verb M" form requires past tense):

**Subtract:** lost, gave, gave away, used, spent, ate, dropped, sold

**Add:** gained, got, received, found, earned, picked up, bought

No wildcards. Verbs not in either set cause the sentence to refuse (not wrong).

### No short-circuit path

Per ADR-0137's subsumption directive, the extractor produces a `CandidateInitial`
that flows through the existing graph machinery. No new bypass route was added.

### Negative-result refusal

If N - M < 0, the extractor refuses. Emitting a negative quantity would violate
the solver's non-negative invariant.

## Per-Case Impact

| Case | v2 Barrier | S.3 Effect | Post-S.3 Barrier | Why |
|---|---|---|---|---|
| 0010 | compound_statement | **Shifted** | fraction_operand | Sentence 1 now parses (Yun, 8, paperclips); sentence 2 "1/4 more than" blocks |
| 0012 | compound_statement | No change | compound_statement | "his fish ate half of them" = compound + fraction + coreference |
| 0013 | compound_statement | No change | compound_statement | "uploads 10 one-hour videos each day" = nested embedded quantifier |
| 0016 | compound_statement | No change | compound_statement | "2 more than 5 miles" = comparative arithmetic, not init-mutation |
| 0032 | compound_statement | No change | compound_statement | "draws and colors 10 pictures" = verb conjunction, not init-mutation |
| 0033 | compound_statement | No change | compound_statement | "7 times her age" = multiplier, not init-mutation |

## GSM8K Admission Count

| Metric | Pre-S.3 | Post-S.3 |
|---|---|---|
| Admitted (correct) | 3 | 3 |
| Wrong | 0 | 0 |
| Refused | 47 | 47 |
| Barrier shifted (v2 → v3) | — | 1 (gsm8k-0010) |

Direct admission delta: **0**. gsm8k-0010's sentence 1 now extracts cleanly but
sentence 2's fraction_operand blocks the case from admitting.

## Axis Lane

24 curated cases at `evals/math_capability_axes/S3_compound_initial_mutation/v1/`:

| Category | Count | Gate |
|---|---|---|
| subtract_canonical | 4 | answer == expected |
| subtract_synonym | 7 | answer == expected |
| add_canonical | 4 | answer == expected |
| add_synonym | 5 | answer == expected |
| refusal_negative_result | 2 | answer is None |
| refusal_verb_miss | 2 | answer is None |

All 24 pass, wrong = 0.

## Cross-Lane Regression

- S.1 rate_events: 20/20 pass, wrong = 0
- S.3 axis lane: 24/24 pass, wrong = 0
- GSM8K admission set: {0014, 0018, 0042} (unchanged)

## Deferred

Every other compound shape from the 6 cases:

- **0012**: "his fish ate half of them" — compound + fraction + coreference
- **0013**: "uploads 10 one-hour videos each day" — nested embedded quantifier + temporal
- **0016**: "2 more than 5 miles" — comparative arithmetic expression
- **0032**: "draws and colors 10 pictures" — verb conjunction (single object, multiple verbs)
- **0033**: "7 times her age" — age-multiplier compound

## Evidence

- Parser addition: `generate/math_candidate_parser.py` (`_INIT_MUTATION_RE`, `_init_mutation_candidates`)
- Axis lane: `evals/math_capability_axes/S3_compound_initial_mutation/v1/`
- Tests: `tests/test_adr_0136_S3_compound_initial_mutation.py`
