# Extract Invariants > Turn a borrowed metaphor, analogy, or cross-domain inspiration into a testable mechanism, or prove it is decoration and discard it. Use when a design leans on language from another field ("immune system", "evolution", "market", "quorum", "crystallization"), when someone proposes copying how another domain solves a problem, or when reviewing a system whose names sound deeper than its code. Produces either a named domain-free invariant with evidence and falsifiers, or an explicit rejection with the reason it failed. - Skill: `ariaxhan/extract-invariants` (Agent Skill) - Install (CLI): `npx skillmds@latest add ariaxhan/extract-invariants` - Raw SKILL.md: https://api.skillmd.com/api/skills/ariaxhan/extract-invariants/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Coding & Dev Tools - Author: ariaxhan (https://skillmd.com/u/ariaxhan) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/ariaxhan/extract-invariants --- # Extract Invariants Metaphors are how good ideas travel between domains, and also how decorative complexity sneaks into systems. The failure mode is consistent: a compelling name ("immune memory", "pheromone trails", "energy minimization") gets an API before anyone checks whether a distinct mechanism exists under it. Months later the code performs elaborate ceremony that reduces to a cache, a counter, or nothing at all. This skill is the gate. A borrowed idea passes only as a domain-free mechanism; the vocabulary it arrived in never ships. ## The test in one line If the idea still needs its source-domain noun to sound meaningful, it has not been abstracted yet. ## 1. State the phenomenon plainly Write down what the source system actually does, in the source domain's own terms. One paragraph. No implications for your system yet. Example: "Black holes have event horizons: regions where causal influence flows in one direction only." ## 2. Strip every domain noun Rewrite the phenomenon with all source-specific vocabulary removed. Every noun must be generic: boundary, log, score, budget, gate, copy, signal, decay. - "Event horizon" becomes "an irreversible causal boundary: information may cross in one direction and never back." - "Immune memory" becomes "a pattern store keyed by past attacks, with faster response on re-encounter and gradual decay." - "Pheromone trail" becomes "a shared score that successful paths increment and time decays." If the rewrite says nothing, stop: you had a mood, not a mechanism. Record the rejection and why. ## 3. Extract the smallest invariant Reduce the stripped description to the minimal relationship that must hold, plus its necessary conditions. Ask: what is the smallest claim that, if false, kills the idea? Format: - **Invariant**: the domain-free claim. - **Necessary conditions**: what must be true of any system for the invariant to apply. - **Tradeoffs**: what enforcing it costs. - **Failure modes**: how systems that rely on it break. ## 4. Demand independent recurrence One domain is an anecdote. Search for the same invariant, independently evolved, in at least two unrelated domains (biology and markets; distributed systems and law; ecology and open source). Kill rule: no recurrence across genuinely unlike domains within a bounded search, then classify it as an interesting metaphor and stop. Recurrence is the evidence. Convergent evolution under similar constraints is what separates an organizational law from a poetic resemblance. Beware the near-miss: two domains that share ancestry (two internet communities, two mammal species) are one domain for this test. ## 5. Check it is operational and falsifiable A surviving candidate must answer all three: - **Instantiation**: what is the smallest software or process change that implements it? Name the concrete primitive (append-only log, quarantine boundary, expiring authority, reputation score, selection loop). - **Falsifier**: what observation would prove it wrong or useless here? - **Cost of being wrong**: what breaks if you adopt it and the invariant does not actually hold in your system? No falsifier means it is faith, not design. Reject or park it. ## 6. Record the verdict either way Write the outcome where future work will find it: - **Admitted**: invariant, conditions, tradeoffs, failure modes, domains observed, proposed instantiation, falsifier, confidence. - **Rejected**: the candidate, which step killed it, and the one-line reason. Rejections prevent the same metaphor from being re-excavated every quarter. The record is the deliverable. An extraction that lives only in the conversation will be repeated, badly, by someone else. ## Worked warning: how it fails without the gate A real system built "crystallographic structure factors" for measuring code quality: complex numbers, phase agreement, R-factors, three hundred lines. Under review, the machinery computed its elaborate score, then overrode it with the raw test-failure rate whenever the two disagreed. The metaphor had an API; the mechanism was a division. The same system's "pheromone-based coordination" scored answers by character length. The tell in both cases: the vocabulary was doing the persuading. Strip the names and read what the code does. When the names carry the meaning, this skill was skipped. ## Anti-patterns - **Metaphor-as-API**: naming modules after the source domain. Names should describe the mechanism (pattern-cache, decay-score), never the inspiration. - **Recurrence by ancestry**: citing sibling domains as independent evidence. - **Poetic invariants**: claims with no possible falsifier ("systems seek balance"). - **Batch romanticism**: importing a whole source domain at once. Invariants pass one at a time, each with its own evidence. - **Skipping the rejection record**: unrecorded rejections guarantee re-litigation.