Lean Proof: The Six-Sphere Has a Complex Structure

Formalization of the Solution to the Hopf Problem

A GitHub repository by Boris Alexeev formalizes the resolution of the Hopf problem in the Lean theorem prover, showing that the six-sphere admits a complex manifold structure compatible with its standard topology. The proof is based on a paper by Levent Alpöge, and the repository includes a comparator setup adapted from Google DeepMind's Formal Conjectures project. The code can be type-checked online.

The six-sphere admits a complex manifold structure compatible with its standard topology.
  1. nhatcher

    Oh wow, I'm fairly impressed. I wouldn't have expected AI to solve a problem this hard just now.

    There have been claims of complex structures on s6 (or absence of them) quite a few times over the last 15 years. Some by acclaimed mathematicians.

    There was some discussions on HN a few days ago:

    https://news.ycombinator.com/item?id=49412947

  2. GPerson

    Surprisingly the (a, since multiple things have this name) Hopf conjecture was solved by human mathematicians around the same time. It’s the statement that S^2 x S^2 admits a positive sectional curvature Riemannian metric.

  3. VMG

    `solution.lean` is a 12mb file

    I looks like we are breezing past the point where unassisted humans can understand any of this

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2026-08-31