FAQ

What is this site?

A collection of open problems in mathematical logic — set theory, model theory, proof theory, computability theory, and related areas. Each problem has its own page with a precise statement, its current status, definitions of the terms it uses, known partial results, and references.

What do the statuses mean?

• Open — unresolved, as far as we know.
• Closed — resolved, with a generally accepted proof.
• No consensus — a proof has been claimed but is not yet broadly verified or accepted.

What do the exclamation marks (impact) mean?

They rate expected impact — roughly, how much the community would be expected to care if the problem were resolved — rather than pure difficulty. Difficulty plays a role, but a problem can be very hard without being especially consequential, or important without necessarily being the hardest thing in its area.

• ! — notable. Every problem listed on this site, including single-exclamation-mark ones, is a genuine, worthwhile open problem — this rating is not a judgment that a problem is trivial or unimportant.
• !! — substantial: resolution would likely be publishable in a strong journal (Advances-level or above).
• !!! — landmark: resolution would be of award-level significance.

This rubric is inherently subjective — treat it as a rough guide, not a strict rule.

What problems can be included?

As a rule of thumb, a problem should have appeared in a published paper or book. We make exceptions for problems appearing only in preprints or other unpublished sources, provided a brief justification is given — this is asked for directly when you submit a new problem.

How do I suggest an edit to a problem?

Every problem page has an editor where you can revise its details and prose, add a short description of your change, and submit it for review. You do not need a GitHub account. Changes are reviewed by the maintainer before they go live.

How do I propose a new problem?

Use Submit a New Problem. You’ll fill in the same kind of structured details (area, impact, reference, etc.) plus a note on where the problem was published. It goes through the same review process as edits before appearing on the site.

Can I comment on a problem?

Yes — each problem page has a comment section. A lightweight sign-up (no GitHub account needed) is required to post.