if there’s one thing we can learn from the history of geometry, it’s that you shouldn’t admit a new axiom into your book until it really proves its worth. Always be skeptical when someone tells you they’re “just being logical.” If they are talking about an economic policy or a culture figure whose behavior they deplore or a relationship concession they want you to make, and not a congruence of triangles, they are not “just being logical,” because they’re operating in a context where logical deduction—if it applies at all—can’t be untangled from everything else. They want you to mistake an
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