# Reasoning Semiformally

> Apply semi-formal certificate reasoning to code analysis — patch verification, fault localization, patch equivalence. Use when reviewing patches, hunting bugs across scopes, comparing fixes, or when code reasoning requires tracing execution across files/modules. Triggers on code review, bug localization, patch comparison, name shadowing, scope analysis, regression checking.

- Skill: `oaustegard/reasoning-semiformally` (Agent Skill, multi-file: 5 files)
- Install (CLI): `npx skillmds@latest add oaustegard/reasoning-semiformally`
- Raw SKILL.md: https://api.skillmd.com/api/skills/oaustegard/reasoning-semiformally/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: oaustegard (https://skillmd.com/u/oaustegard)
- Updated: 2026-09-10
- Page: https://skillmd.com/skills/oaustegard/reasoning-semiformally

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# Semi-Formal Code Reasoning

Structured certificate templates that force mandatory checkpoints before conclusions.

## Skip Conditions

Do NOT apply semi-formal reasoning when:
- The change is trivial: docs, formatting, version bumps, config changes
- The bug is locally obvious: typo, off-by-one in the same function, missing comma
- No execution paths cross scope boundaries
- The task is not code analysis (text editing, data extraction, summarization)

If any skip condition is met, proceed with standard reasoning.

## Model-Specific Instructions

**If you are Haiku-class (Haiku 4.5 or similar):**
Read `haiku.md` in this skill directory. It contains full procedural templates with worked examples.

**If you are Sonnet-class or above (Sonnet 5, Opus):**
Read `sonnet.md` in this skill directory. It contains compact verification checkpoints.

## Composing Tasks

For complex tasks, apply templates sequentially:
1. **Fault localization** to find the bug
2. **Patch verification** to validate a proposed fix
3. **Patch equivalence** to compare alternative fixes

Each output feeds the next as premises.