Section 11.9: restrict Ex. 11.9.1 to interior rationals from issue #517#531
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teorth merged 1 commit intoJun 15, 2026
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DifferentiableWithinAt on Icc 0 1 is one-sided at the endpoints. Co-authored-by: Cursor <cursoragent@cursor.com>
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rkirov
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Jun 14, 2026
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Summary
Fis not differentiable withinIcc 0 1at every rational in[0,1].DifferentiableWithinAton a closed interval is a one-sided condition at endpoints, soFis differentiable atq = 0andq = 1.Root cause
The formalization used
q ∈ Icc 0 1, which includes endpoints where the negated differentiability claim is false.Fix
Require
q ∈ Ioo 0 1, matching Tao's intent for interior rationals.Test plan
lake build Analysis/Section_11_9.leanFixes part of #517.
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