# A Proof-Library

Is there any source, perhaps a website or a book, which keeps track of all different proofs ever announced of a theorem? For example, I have heard that there are about $80$ different proofs of the Pythagorean Theorem. I am more interested in Niven's Theorem, which deals with the rationality of the trigonometric functions at the rational multiples of $\pi$. Can anyone suggest me where I can find all proofs of the result announced to date?

• Have you been to www.proofwiki.com? I think they have lots of proofs – Logan Tatham Feb 19 '14 at 17:00
• @LoganTatham, you mean this...proofwiki.com – Indrayudh Roy Feb 19 '14 at 17:07
• Yeah, I doubt you will find a complete list anywhere - even the 80 proofs of Pythagorean Theorem makes no assertion of completeness. – Thomas Andrews Feb 19 '14 at 17:28
• @ThomasAndrews, I don't want the Pythagorean Theorem, but Niven's Theorem, which is not as popular as that of Pythagoras', and must have a much fewer number of proofs than of Pythagoras' and it is perhaps somewhere. – Indrayudh Roy Feb 19 '14 at 17:32
• I didn't mean that, I meant that there was no such compendium for Pythagorean theorem, a major theorem, so it was unclear why there'd be such a compendium for a (relatively) minor theorem... – Thomas Andrews Feb 19 '14 at 18:04