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Frequently Asked Questions

When I open a theorem it opens in Acrobat instead of in my browser. How can I change this?
It will probably be a preference or options setting in your browser. For instance in my version of Firefox it is the Applications tab under Options and then scroll down to "Portable Document Format (PDF)". It should say "Use Adobe Acrobat (in Firefox)": if the "(in Firefox)" is missing then click on it and select that option.

What does it mean that you claim Theorem of the Day is "Tau manifesto compliant"?
You can read about this here. I would be interested to hear what you think — email me with your views!

Does Theorem of the Day use cookies?
Not directly but some widgets/scripts incorporated into some pages may generate and/or store information on your computer. Read more here.

Can I use text and images from Theorem of the Day pages?
You are free to make whatever non-commercial use you like of any of the material found at this site except text/images which are reproduced with permission (as mentioned on individual pages and see Acknowledgements). Of course, I would be happy if was mentioned as the source.

Is visiting the only way to see today's theorem?
No, the URL supplies a direct link to today's theorem; loads the theorem into a browser page (it uses frames and javascript). More details are given on our resources page.

Why do the theorem descriptions not have proofs?
A few do (e.g. Euclid's Infinity of Primes, and the Contraction Mapping Theorem) and these are marked with a 'QED' in the main theorem listing; but mostly a proof, or even a sketch proof, would be far too long for the 1-page format (e.g. the Robertston–Seymour Graph Minors Theorem whose proof is over 500 pages long). Wherever possible the recommended web link points to an article or web page giving a proof. And checking Wikipedia is an option which needs no introduction.

Does Theorem of the Day have a regular newsletter or mail shot?
There is no plan at present to contact people directly with information, even about new theorems, but you can subscribe to our rss newsfeed or follow us on Twitter to get updates (see resources). I do keep an email circulation list for special events and you are welcome to send your details to me for that purpose.

Are the theorem descriptions refereed?
Definitely not to the same standard as a maths journal! I have almost always had theorem descriptions checked by experts in the areas concerned but this does not mean they have had time to check the accuracy of examples, historical references, etc. A list of those who have helped me get things right can be found at the beginning of the list of Acknowledgements.

Do you actually prepare a new theorem every day?
No! A theorem a month is the best I might aim for presently — I posted 11 theorem descriptions in 2013. It sometimes takes me a long time to understand a theorem well enough to construct a concrete illustration of it. And if I'm sensible I wait for feedback from at least one expert before posting a description. "Rome wasn't built in a day," I told my daughter, to which she replied sternly, "Well, it should've been!"

How do you choose the theorems?
I will have a go at anything which catches my imagination. Sometimes people are kind enough to make suggestions. The theorems chosen have to be 'iconic' in some sense; the only other criterion is that it has to be possible to produce a concrete illustration — alas this puts a lot of beautiful mathematics beyond my reach!

What is your target audience?
Ah — this website is a 'gallery' so it doesn't have to have a target audience! Anybody is welcome to come in and derive what pleasure or instruction they may. I shudder to think that art galleries and museums today probably do in fact have to define and justify their 'target audiences' for the bean counters. A similar issue is raised forcefully by No to Age Banding a campaign which has my great sympathy.

How is a theorem chosen for a particular day?
The ordering is more or less random. The mechanics are explained here. There are a few influences: International Women's Day will be marked by a theorem from the list of Theorems by Women Mathematicians, as will Ada Lovelace Day and Tau Day is marked by a theorem about Tau.

Why does do a 'theorems by women' calendar?
Currently I don't ... I haven't had the time to produce theorem descriptions fast enough, alas, to collect 12 new theorems by women per year. I could do a generic 'beautiful theorems' calendar but I thought one highlighting women's achievments might do some good and certainly wouldn't compromise the quality of theorems on offer. I am not an expert but it seems that women are still very under-represented in mathematics. See here for more.

When I display a theorem the images are blurred. Why?
I don't know. I think it is browser specific and maybe machine specific.Here are a couple of fixes:
Internet Explorer: hit the back arrow and then the forward arrow: it usually reloads properly.
Firefox: increase the size of the display in the pdf toolbar by one or two percent.


Theorem of the Day is maintained by Robin Whitty. Comments or suggestions are welcomed by me.
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