Using Lemma

Who can use Lemma

You must be 13 or older. If you are under 18, use Lemma with a parent's or guardian's permission and show them the note for parents.

Your account

You sign in through Clerk, by email or with Google. Keep your login to yourself; you are responsible for what is posted from your account.

What you post

Solutions, problems and comments you post stay yours. You give Lemma permission to show them on the site, and to anyone you share a link with. Don't post other people's work as your own, anything you don't have the right to share, or anything abusive. We may remove content and close accounts that break these rules.

The checker is an AI, and it can be wrong

“Check your work” uses AI models to read and judge your solution. It can pass work that is wrong or miss a correct method. Treat its verdict as a second opinion, not a grade, and never as an official result for an exam or competition. A share link that says “Checked by Lemma” means only that.

AI-drafted teaching text

Primers and some walkthroughs are written by AI and labelled “AI-drafted”. The problems come from people and from public-domain or openly licensed books, credited on each problem.

Open content stays open

Material from openly licensed sources, such as Strang's Calculus (CC BY-NC-SA), stays under its licence and is never behind a paid plan. The reading roomlinks to works on their authors' own sites; their terms apply there.

Lemma Plus

Lemma Plus is a subscription, billed monthly or yearly through Stripe. You can cancel at any time from the Plus page; your subscription runs to the end of the period you paid for, and isn't refunded for the part already started unless the law requires it.

Fair use

Don't try to overwhelm, scrape or reverse-engineer Lemma, or get around its daily limits. Automated or abusive use may be limited or blocked.

No warranty

Lemma is provided as it is, without warranties of any kind, and may change or stop. To the extent the law allows, Lemma isn't liable for indirect or consequential losses, or for decisions you make based on a check.

Changes

We may update these terms; the date at the top shows when. You can stop using Lemma and ask us to delete your data at any time.

Contact

Questions? Email support@lemmaproof.com.