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skills/code-comparison/SKILL.md

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+# Code Comparison
+
+Compare code implementations for equivalence, similarity, or differences with accurate classification.
+
+## Comparison Dimensions
+
+| Dimension | Question |
+|-----------|----------|
+| **Behavioral** | Same outputs for same inputs? Same side effects? |
+| **Semantic** | Same intent/purpose? Same business logic? |
+| **Syntactic** | Similar names, structure, formatting? |
+| **Algorithmic** | Same approach? Same complexity (Big O)? |
+| **Style** | Functional vs imperative? Recursive vs iterative? |
+
+## Common Scenarios
+
+| Scenario | Focus |
+|----------|-------|
+| Refactoring | Behavioral equivalence (must match) |
+| Bug fix | Specific case differs, normal matches |
+| API compat | Signature, returns, errors, side effects |
+| Plagiarism | Structure, naming, logic patterns |
+
+## Output Format
+
+Start with **[YES]** or **[NO]** immediately.
+
+Then provide justification with specific examples from both items.
+
+## Analysis Checklist
+
+- [ ] Inputs (same params, types?)
+- [ ] Outputs (same returns?)
+- [ ] Side effects (same state changes?)
+- [ ] Error handling (same exceptions?)
+- [ ] Edge cases (null, empty, boundary?)
+- [ ] Performance (same complexity?)
+
+## Example
+
+```
+[YES] Behaviorally equivalent
+
+Both functions:
+1. Return same results for all inputs
+2. Handle null by returning empty array
+3. Use same filtering logic
+
+The refactoring improves readability (modern array methods) without changing behavior.
+```
+
+## Pitfalls
+
+- Don't stop at surface differences (naming != different behavior)
+- Check edge cases (factorial(-1) may differ)
+- Consider context (Promise vs callback may be equivalent in modern Node)