Terms of sale

Art of DS (“the site”, “we”, “us”) is run by Vladyslav Kaptenko. You can reach us at support@artofds.com.

These terms apply when you create an account or get lifetime access. The Privacy policy, the Refund policy and the Cookies page are part of them. Reading the free pages needs no account.

You sign in with your email address: we send a link and a six-digit code, and there is no password. Whoever can read that mailbox can sign in as you, so keep it to yourself.

An account is for one person, aged 16 or over. Do not share it, and do not sell or lend access to it.

Lifetime access is one payment that unlocks everything on the site that is not free:

• every page in full, including the pages added later;
• the quiz on every page and the final test, saved to your account;
• certificate attempts at the final test, and a certificate with your name when you pass;
• your progress — the pages you have read, where you stopped, your quiz results and your streak — synced across your devices.

It is not a subscription: nothing renews and nothing is charged again.

Lifetime access costs $20 (US dollars), once, with any tax that applies where you live shown at checkout.

Our order process is conducted by our online reseller Paddle, the merchant of record for all our orders. Paddle takes the payment, handles the tax and issues your receipt, under its own buyer terms; we never see your card details.

A promo code that takes 100% off gives the same lifetime access as a payment. A code has no cash value and can be used once per account.

Access starts as soon as the payment is confirmed. “Lifetime” means for as long as we run Art of DS; if we ever close it, we will tell you by email at least 60 days before.

What anyone can read without an account — the free pages, the definition, formula, intuition and sources of every other page, and the catalogues — is published under the Creative Commons Attribution-ShareAlike 4.0 licence (CC BY-SA 4.0): you may share and adapt it, commercially included, crediting Art of DS and passing the same licence on.

What lifetime access unlocks — the rest of those pages, with their figures and worked examples, and their quizzes — is ours, with all rights reserved. Read it, study it, keep notes, use what you learn, and quote short passages with a link; do not republish it or make it available to others, as it is, translated or adapted. The code in the worked examples is under the MIT licence wherever it appears. The About page sums this up.

Do not share your account, get around the locks on the site, or send automated requests at a rate that burdens it. We may suspend an account that does, after telling you why.

Art of DS is a reference for learning. We take care that every claim is sourced and every worked example was run, but the site may still contain mistakes, and nothing on it is professional advice. If you find an error, tell us at support@artofds.com.

Nothing here limits the rights you have as a consumer where you live. Beyond them, our liability to you is limited to what you paid.

If these terms change, the new version is published here with its date, and if a change affects what you bought, we will email you before it applies. A change never takes away what you have already paid for.