core/docs/briefs/parallel-2026-05-23/L10-ADR-0131-G2-comparatives.md

L10 brief — ADR-0131.G.2 — Capability axis: comparatives (additive + multiplicative)

Worktree setup (do this first, non-negotiable):

git worktree add ../core-adr-0131-g2-comparatives -b feat/adr-0131-g2-comparatives origin/main
cd ../core-adr-0131-g2-comparatives

Scope. Capability-axis iteration: land candidate emitters for compare_additive and compare_multiplicative. The round-trip verb tables (COMPARE_ADDITIVE_ANCHORS, COMPARE_MULTIPLICATIVE_ANCHORS) and the Comparison operation shape (generate/math_problem_graph.py:128) already exist — what's missing is the candidate-parser side. The comment at generate/math_candidate_parser.py:30 explicitly flags this as a deferred phase.

Comparatives are an operation kind the binding graph already admits; the architectural extension is purely on the parse side. Target shapes (closed set):

• Additive: <EntityA> has N more <unit> than <EntityB>, <EntityA> has N fewer <unit> than <EntityB>, <EntityA> has N additional <unit>.
• Multiplicative: <EntityA> has twice as many <unit> as <EntityB>, <EntityA> has N times as many <unit> as <EntityB>, <EntityA> has half as many <unit> as <EntityB>.
• Nested compositional (load-bearing — appears in baseline refusal Jen has 10 more ducks than four times…): <EntityA> has N more <unit> than M times <EntityB>'s <unit>. Treat as a composed compare_additive(EntityA, compare_multiplicative(EntityB, M)) structure.

Reference docs (read these, only these):

1. docs/decisions/ADR-0131.G-gsm8k-coverage-probe.md — iteration discipline (single axis, own coverage cases, GSM8K admission strictly increases or a refused-reason family is deliberately reduced, admitted_wrong == 0).
2. generate/math_problem_graph.py (Comparison) + generate/math_roundtrip.py (anchor tables) — the contract the new emitter must satisfy. Do not redefine direction vocab; emit into the existing four direction ∈ {more,fewer,times,fraction} slots.

What to ship:

• Parser extension in generate/math_candidate_parser.py: new _compare_additive_candidates / _compare_multiplicative_candidates extractors emitting CandidateOperation records whose op.kind is compare_additive / compare_multiplicative. Regex specificity order documented; nested composition produces two candidates and the round-trip layer / binding graph (Phase 3, ADR-0134) picks the admissible composition.
• Curated coverage cases at evals/math_capability_axes/G2_comparatives/v1/cases.jsonl (~25 cases): ≥4 per direction (more, fewer, times, fraction) + ≥3 nested-composition cases + ≥4 refusal cases for paraphrases outside the closed set (e.g. "as many … as", "compared to", "in comparison with"). The refusal cases pin the scope boundary.
• Runner + report at evals/math_capability_axes/G2_comparatives/v1/.
• Tests at tests/test_adr_0131_G2_comparatives.py (~12): per-direction at-least-one passing, nested-composition at-least-one passing, refusal cases all refuse with typed parser error, wrong == 0, replay byte-equality, GSM8K probe re-run with admission_rate strictly increases OR refused_reasons_top for comparative-shape clauses strictly decreases (whichever is honest — pick one in the ADR and gate on it).
• ADR docs/decisions/ADR-0131.G.2-comparatives.md. Document closed-set anchor alternation; explicitly call out which paraphrases are deferred and why (they are not in the round-trip table either — admitting them would breach wrong == 0).
• Refresh evals/gsm8k_math/train_sample/v1/train_sample_coverage_report.json.

Hard constraints:

• Direction vocab is closed to the four Comparison.direction literals. No new literals.
• wrong == 0 on the new axis and the probe. Nested-composition admissibility is the round-trip layer's job — do not bypass it.
• No solver / binding-graph changes. If a comparative parses but does not solve, that's a downstream gap → file it as a follow-up ADR, do not stub the solver.
• Specificity order documented. Multiplicative anchors that overlap with additive (twice vs two more) must have deterministic precedence pinned in the ADR.
• No new modules under algebra/, chat/, core/.
• Determinism. Report byte-equal across runs.

Out of scope: verb classes for initial state (L9/G.1), rate verbs (L11/G.3), multi-clause distributive subjects (L12/G.4), implicit-comparison shapes ("the same number of … as").

Target branch. PR against main. Title: feat(ADR-0131.G.2): comparative operations (additive + multiplicative) — admission N/50 (Δ+N). Body: per-direction case counts, refusal-set documentation, admission delta or refused-reason-family delta, link to ADR.

Exit criterion. CI green; comparatives runner exits 0 with wrong == 0; chosen GSM8K-probe gate (admission ↑ OR comparative-clause refusals ↓) satisfied; B3 + L9/G.1 axis lanes unchanged; refreshed coverage report committed.

Do not stack on another agent's branch. Target main directly.