MathsClub Problems, proofs & good company

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.

Tagged independence — 2 entries. Clear

Does the countable chain condition characterise ℝ? Independent of ZFC: Suslin lines exist under V = L, consistently none exist (Solovay–Tennenbaum 1971).

Posed by Mikhail Suslin · 1920 · set theory / foundations · difficulty 4/5

independence

Is there a cardinality strictly between the integers and the reals? The first Hilbert problem dissolved into independence: yes in Gödel\'s universe, no in Cohen\'s — and both are legitimate.

Posed by Georg Cantor · 1878 · set theory / foundations · resolved 1963 · difficulty 5/5

independence