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4. Printing
Gutenberg solved the technical challenge of replacing monks doing calligraphy with machines that could faithfully replicate words on a page. But the value comes from a deeper insight: When we can share the world's ideas cheaply, we all make progress vastly more efficiently. And ideas, remember, are “neg-entropic”: I can use an idea, and so too can you, and they get better organized, more refined, and cumulatively more valuable over time.
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