Last update: May 20, 2025
About the web site Differential Geometry
Differential Geometry, operated by freelance mathematician Andrew D. Hwang (“I”), is an online shop that sells original mathematical jewelry and sculpture, original mathematical designs printed on wall art, clothing, and other items. The site also hosts a math blog whose aim is to promote understanding and appreciation of mathematics and mathematical beauty.
Below, the terms “we” and “our” refer to the company, Differential Geometry LLC, that I own and operate. “Differential Geometry” and “our site” refer to this web site.
Principles and summary
As a business and web site, Differential Geometry is devoted to mathematics, mathematical design, and mathematical education and outreach. We do not obtain revenue from advertising other web sites. We do not deploy third-party analytics to track your activities here or elsewhere. We do not use AI to generate text or images, and do not knowingly use AI for any purpose.
Privacy, which is among my highest concerns, encompasses protecting your personal data by strong encryption, by secure handling and storage, and to the extent of my ability, by stringent avoidance of third-party services that deploy and profit from tracking analytics.
Data we collect and store
We collect and store personal data as necessary to ship orders you place and ensure they arrive in good condition; and to fulfill our own legal obligations, such as collecting sales tax and maintaining accounts.
Purchases
Name and address: When you make a purchase at Differential Geometry, we require you to provide your name, shipping address, and an email address or telephone number. Your shipping address is used to calculate taxes and shipping charges, and to deliver your order. Your email address or telephone number are used in case we need to communicate with you regarding the status of your order. These personal data are not used for any other purpose.
Payment information: When you make a purchase at Differential Geometry, you must supply payment details, such as a credit card number, in the checkout page. Information entered into the payment field of the checkout page is securely collected by our payment processors, not by Differential Geometry.
Depending on your choice of payment method, you may be prompted in the payment area to “create an account”; for example, if you pay by credit card in the US, Stripe may offer to create a Link account to store your payment information securely. Such an account is made with that payment processor, not with Differential Geometry, and is subject to the processor’s privacy policy.
Subscriptions
Shop account: At checkout, you may optionally create a shop account to securely store your name and address (“profile”) for use with future purchases. If you are logged in to your shop account, your profile is used to populate the check-out page with your name and address. Your profile is used for no other purpose. Creating a shop account does not subscribe you to receive shop emails.
Email lists: If you subscribe to one or more of the shop’s email lists, we securely collect and store your email address and optionally your first and last name. We use your subscribed email address to send human-authored informational and promotional list messages, typically no more than once per month, and for no other purpose. You may unsubscribe yourself from our email lists at any time.
Visiting the Site
HTTP headers: When you visit Differential Geometry, we collect HTTP header data in hashed (anonymized) form, solely for internal use as site statistics.
Cookies: We use cookies to keep track of cart contents while you are browsing our site, and so that you can be shown products you have recently viewed. If you create a shop account, we use cookies to manage your logged in status.
Comments and reviews: If you leave a comment or review, a hashed (anonymized) string created from your email address is provided to the Gravatar service to see if you are using it. Please see the Gravatar service privacy policy (external site) for details. After approval of your comment, your Gravatar profile picture is visible to the public in the context of your comment. Comments and reviews are subject to being indexed by search engines.
We store and display comments and reviews indefinitely. If you wish to remove one of your own publicly-visible comments or reviews, we will make a good faith effort to comply, though we reserve the right not to do so.
What we share with others
Except as required by law, we do not share your name, email, or other personal information with any third party for any purpose except fulfilling our obligations to you: Shipping orders to you, and sending emails for which you have opted in.