logic-diff · diff

git:20260429.db6dc75 to git:20260502.677a485

1 added, 1 removed. Audit A to A.

---

name: logic-diff

description: >

Compare two code versions for semantic equivalence via semi-formal tracing

of both versions side-by-side. Trigger when the user shares a refactor,

rewrite, migration, or A/B implementation and wants to confirm behavior

is unchanged — "did I break anything", "is this equivalent", "check my

refactor", "same behavior after the change?", "does my rewrite produce

the same output", "switched from X to Y — same results?".

SCOPE HARD RULE: requires two code versions (A and B). A single version

for bug-finding uses logic-review; one version + a failing test uses

logic-locate; explaining what one piece of code does uses logic-explain;

codebase audit uses logic-health.

Do NOT trigger for: single-version review, performance comparison,

design-quality comparison, or "which is better-written" questions.

---

# Logic-Lens — Semantic Diff

## Setup

Read in this order:

1. `../_shared/common.md` — language rule, Iron Law, Report Template, Verdict header (see §5), Remedy discipline.

2. `../_shared/logic-risks.md` — L1–L9 definitions (used to classify divergences).

3. `../_shared/semiformal-guide.md` — tracing methodology.

4. `../_shared/semiformal-checklist.md` — Premises Construction Checklist.

5. `../_shared/report-template.md` — Report layout (English + Chinese).

6. `logic-diff-guide.md` — comparison process.

## Process

**Step 0. Language + scope routing.** Detect language per `common.md` §1. Confirm two versions are provided. If only one version, switch to logic-review.

- **Step 1. Identify the shared specification** (guide Step 1) — what inputs should both versions handle; what outputs/side effects are expected.

+ **Step 1. Identify the shared specification** (guide Step 1) — what inputs should both versions handle; what outputs/side effects are expected. If the user states the refactor intentionally changed behavior in a specific area (e.g., "I changed the error path to raise instead of returning None"), record that as a **declared spec change** and treat divergences within that area as expected. Flag only divergences outside the declared change as findings.

**Step 2. Build independent premises for each version** (guide Step 2) — apply the Premises Construction Checklist to Version A and Version B separately.

**Step 3. Trace both versions for the common case** (guide Step 3) — parallel trace, same input, note the first divergence if any.

**Step 4. Trace boundary cases** (guide Step 4) — empty/null/zero, max/min, error inputs, first/last of collections.

**Step 5. Identify and classify semantic divergences** (guide Step 5) — each divergence is a finding with Premises → Trace → Divergence → Remedy and an L-code.

**Step 6. Equivalence verdict** (guide Step 6) — one of: `✅ Semantically Equivalent`, `⚠️ Conditionally Equivalent` (state the condition precisely), `❌ Semantically Divergent`.

**Step 7. Output** (guide Step 7) — Report Template with the Verdict header per `common.md` §5; localize headers if the user wrote in Chinese.

**Mode line in report:** `Semantic Diff` (Chinese: `语义对比`).