The Conway knot is not smoothly slice

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conway_knot_not_smoothly_slice

Submitter: Kim Morrison.

Notes: Lisa Piccirillo, *The Conway knot is not slice*, Annals of Mathematics 191 (2020). Resolves the last remaining case in the classification of slice knots through 12 crossings. The Conway knot has trivial Alexander polynomial so is topologically slice (Freedman), while Piccirillo's theorem rules out smooth sliceness — pairs with `conway_knot_topologically_slice` for an explicit, low-crossing-number witness to the smooth/topological gap (earlier witnesses such as Akbulut-Matveyev's Whitehead doubles existed).

Source: https://arxiv.org/abs/1808.02923

Informal solution: Piccirillo's strategy: construct a knot K' having the same 0-trace as the Conway knot. The trace-embedding argument then transfers sliceness — if the Conway knot were smoothly slice, K' would be too. Compute Rasmussen's s-invariant of K' (a smooth slice obstruction, via Khovanov homology / Lee's perturbation); show s(K') != 0; conclude both K' and the Conway knot are not smoothly slice. Note that the standard smooth slice obstructions s and tau both vanish on the Conway knot itself, which is why the detour through K' is needed.

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