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natural-transformations

Provides a decision tree to verify naturality and diagram commutativity in category theory using Lean 4 syntax.

Install

mkdir -p .claude/skills/natural-transformations && curl -L -o skill.zip "https://agentskills.codes/api/skills/download/2323" && unzip -o skill.zip -d .claude/skills/natural-transformations && rm skill.zip

Installs to .claude/skills/natural-transformations

Activation

This is the description your AI agent reads to decide when to run this skill — the better it matches your request, the more reliably it fires.

Problem-solving strategies for natural transformations in category theory
73 charsno explicit “when” trigger
Advanced

Key capabilities

  • Verify naturality of transformations between functors
  • Define natural transformations using Lean 4 syntax
  • Perform vertical and horizontal composition of transformations
  • Apply the Yoneda lemma for functor embedding
  • Check for natural isomorphisms

How it works

The skill provides a decision tree for verifying naturality diagrams and maps these concepts to Lean 4 syntax and Mathlib library functions.

Inputs & outputs

You give it
Functor definitions and diagram commutativity requirements
You get back
Lean 4 theorem proofs or transformation definitions

When to use natural-transformations

  • Verify naturality diagrams
  • Define natural transformations in Lean
  • Apply Yoneda lemma
  • Perform component analysis

About this skill

Natural Transformations

When to Use

Use this skill when working on natural-transformations problems in category theory.

Decision Tree

  1. Verify Naturality

    • eta: F => G is natural transformation between functors F, G: C -> D
    • For each f: A -> B in C, diagram commutes: G(f) . eta_A = eta_B . F(f)
    • Write Lean 4: theorem nat : η.app B ≫ G.map f = F.map f ≫ η.app A := η.naturality
  2. Component Analysis

    • eta_A: F(A) -> G(A) for each object A
    • Each component is morphism in target category D
    • Lean 4: def η : F ⟶ G where app := fun X => ...
  3. Natural Isomorphism

    • Each component eta_A is isomorphism
    • Functors F and G are naturally isomorphic
    • Notation: F ≅ G (NatIso in Mathlib)
  4. Functor Category

    • [C, D] has functors as objects
    • Natural transformations as morphisms
    • Vertical composition: Lean 4 CategoryTheory.NatTrans.vcomp
    • Horizontal composition: CategoryTheory.NatTrans.hcomp
  5. Yoneda Lemma Application

    • Nat(Hom(A, -), F) ~ F(A) naturally in A
    • Lean 4: CategoryTheory.yonedaEquiv
    • Fully embeds C into [C^op, Set]
    • See: .claude/skills/lean4-nat-trans/SKILL.md for exact syntax

Tool Commands

Lean4_Naturality

# Lean 4: theorem nat : η.app B ≫ G.map f = F.map f ≫ η.app A := η.naturality

Lean4_Nat_Trans

# Lean 4: def η : F ⟶ G where app := fun X => component_X

Lean4_Yoneda

# Lean 4: CategoryTheory.yonedaEquiv -- Yoneda lemma

Lean4_Build

lake build  # Compiler-in-the-loop verification

Cognitive Tools Reference

See .claude/skills/math-mode/SKILL.md for full tool documentation.

When not to use it

  • Tasks unrelated to category theory
  • General programming logic not involving functor mappings

Prerequisites

Lean 4Mathlib

Limitations

  • Requires Lean 4 environment for verification
  • Limited to the scope of category theory natural transformations

How it compares

It translates abstract category theory proofs into verifiable Lean 4 code rather than relying on manual diagrammatic reasoning.

Compared to similar skills

natural-transformations side by side with the closest alternatives in the catalog.

SkillInstallsUpdatedSafetyDifficulty
natural-transformations (this skill)27moReviewAdvanced
literature-review5592moReviewAdvanced
openalex-database487moReviewIntermediate
annas-archive-ebooks227moReviewBeginner

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