The Problems

Not schoolwork — the questions that resisted Erdős, Hilbert, and everyone since. The club keeps three shelves: what is still open, what AI recently settled, and what took humanity centuries.

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The Hanna Neumann conjecture historic

How large can the intersection of two free subgroups be? Hanna Neumann asked in 1957; Mineyev and Friedman proved the sharp bound independently in 2011.

· Geometric group theory · resolved 2011 · difficulty 4/5

geometric-group-theory free-groups