'Rationality: From AI to Zombies' is available on a pay-what-you-want basis. It talks about cognitive science, ethics, human (ir)rationality and how to improve it, among other things. It stems from the Lesswrong Sequences [2], which have a lot more content, but are a bit messy. [1] https://intelligence.org/rationality-ai-zombies/ [2] http://wiki.lesswrong.com/wiki/Rationality_materials
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