feat: add Cerf's theorem Γ₄ = 0 eval problem - #17
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Cerf's 1968 theorem: every self-diffeomorphism of S³ is smoothly isotopic to the restriction of a linear isometry of ℝ⁴. Stated as the existence of a smooth isotopy [0,1] × S³ → S³ from f to a linear isometry, with smooth slice-inverse encoding the diffeomorphism property of each time-slice. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Summary
[0,1] × S³ → S³with a smooth slice-inverse, which forces each time-slice to be a diffeomorphism without needing a C^∞ topology onDiffeomorph S³ S³(which mathlib does not yet carry).🤖 Prepared with Claude Code