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“I decided it would be fun to do patent trials,” said Richard Posner.

We were sitting in his spacious office in the federal courthouse in downtown Chicago, where, for more than three decades, Posner, 74, has been a judge on the United States Court of Appeals for the Seventh Circuit. Posner is one of the most prolific writers in the country, not just of legal opinions but of books and articles on a staggering variety of subjects.