Privacy Policy

Last updated October 13, 2026

Lemmas is a study tool. It keeps the record of your practice so it can tell you what to work on next. This page describes exactly what that record contains.

Who runs this service

Lemmas is operated by William Sun and Surya Raghavan, based in New Jersey, US. Questions about this policy go to lemmas.official@gmail.com.

What Lemmas stores

Because you asked it to keep your progress, an account holds:

• Identity: your email address, username, and a scrypt hash of your password. The password itself is never stored.
• Profile you write: a short description, a location field you fill in freely, and your daily and weekly goals.
• Practice record: problems attempted, the answers you selected, whether they were correct, time taken, saved problems, your mistake notebook and the date each missed problem comes back for a re-solve (and, once repaired, the new problem chosen to check it), badges you have earned and which of them you show beside your name, the quests planned for you each day with the XP each one paid, and any problem you reported with the reason you gave.
• What you write for other students: the solutions you post under problems, the “helpful” marks you give, reports you file about a solution, and the posts and votes you make on the Feedback board.
• Friends and sharing: your friend list, the requests you have sent and received, accounts you have blocked, the problems and cards you send and receive with the note you wrote (at most 140 characters), and whether you have left the global leaderboards.
• Your written work: the scratchpad notes you write beside each problem, the geometry sketches you draw, and your reflections on missed problems (the cause you picked and any note you added).
• Planning: your competition track, exam date, weekly minutes, focus subject, and study plan.
• Sessions: for each device you are signed in on, a hash of the session credential, timestamps, and a coarse label such as “Chrome on macOS”.
• Google sign-in, if you use it: the provider name and Google’s stable account identifier. Lemmas does not store Google access or refresh tokens and does not request Drive, Gmail, or Calendar access.
• Product events: a fixed, published allowlist of milestones such as “onboarding completed” or “arena completed”.

What other learners see

Other signed-in learners can open your public page and see your username, level and tier, the badges you chose to show, how many problems you have solved, and your skill shape. The solutions you post are shown, with your username, to learners who have answered the same problem. Your friends also see a calendar of how much you did each day. Nobody sees your email address, your description or location, your answers, your notes or your sketches. Friends can send you problems and cards with a short note, and only friends can; a note cannot carry a link, an email address or a phone number. You can block anyone, which removes you from their view and theirs from yours, and you can leave the global leaderboards in Account and settings; friends still see you. Your username is shown to others, so do not use your real name unless you want it known.

What Lemmas deliberately does not store

• No third-party analytics, advertising, or tracking scripts. There is no Google Analytics, no pixel, and no cross-site identifier.
• No browser fingerprinting.
• No raw IP address. To limit password guessing, Lemmas keeps a salted, one-way digest of the network address alongside a failure count for fifteen minutes. The address itself is never written down and cannot be recovered from the digest.
• No raw User-Agent string. Only the coarse device label described above.
• Your answers and scratchpads are never treated as analytics properties.

Why it is stored

Every item above exists to run the product you signed up for: to grade your work on the server so answers stay private, to recommend the next problem, to schedule formula review, to keep you signed in, and to protect the account from password guessing. Lemmas does not sell personal information and does not share it with advertisers.

How long it is kept

Account data is kept while the account exists. Sessions expire after thirty days and can be revoked sooner from Settings. Rate-limit counters are pruned automatically once their fifteen-minute window passes. Deleting your account removes the record immediately and permanently.

Your control

• Export: Settings gives you one JSON file containing your account data. Password hashes and session credentials are excluded from it by design.
• Correct: profile fields and goals can be changed at any time.
• Delete: Settings permanently deletes the account and everything owned by it. This cannot be undone, and it does not delete your Google account.
• Sign out elsewhere: Settings lists your active sessions and can revoke every device except the one you are using.

Young learners

Competition mathematics has many participants under 18, and some under 13. Lemmas asks for an email address to create an account, which in some jurisdictions requires verifiable parental consent below a certain age. If you are under 13, please ask a parent or guardian to set up and supervise the account. A parent or guardian who wants an account and its data removed can write to lemmas.official@gmail.com and it will be deleted.

Third parties

Lemmas relies on its hosting provider and its database provider to run the service, and on Google only if you choose Google sign-in. No other third party receives your data.

Changes

If this policy changes in a way that affects what is collected or why, the updated date above will change and the change will be described here.

September 26, 2026: the list of what an account holds now names three kinds of your own work that were already kept but not listed here (geometry sketches, problem reports, and honors), and one new one: your reflections on missed problems, with the date each comes back for a re-solve. None of it is shared, and all of it is deleted with your account.

October 11, 2026: honors are now called badges, and there are more of them. Your account also keeps which badges you choose to show beside your name. It is deleted with your account.

October 11, 2026: each day your account now keeps the small set of quests planned for you and the XP each one paid. Your data export includes them, and they are deleted with your account.

October 12, 2026: accounts can now add friends by username, send each other problems and cards, and appear on leaderboards. Your account keeps your friend list, requests, blocks, what you send and receive, and your leaderboard setting, and the section above says what other learners can see. All of it is in your data export and is deleted with your account.

October 12, 2026: students who have answered a problem can now read, and write, solutions to it, and everyone signed in can post on and vote for items on the Feedback board. A solution or a post shows your username and the date, and is visible to other signed-in students; it cannot carry links or contact details. Three reports from different students hide a solution until it is reviewed. What you write is in your data export and is deleted with your account.