Unreasonable Effectiveness of Compositional Thinking → examples → category, functor, natural transformation → Category Theory Example: Applied to a Database → Functor = Dataset →
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A functor $F: \mathcal{C} \to \mathbf{Set}$ assigns:

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$F(\text{Person}) = {\text{Alice},\ \text{Bob}}$

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$F(\text{City}) = {\text{Boston},\ \text{LA}}$

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$F(\text{lives_in}) = {(\text{Alice},\ \text{Boston}),\ (\text{Bob},\ \text{LA})}$

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