A forum for proofs · thethinkingboard.com
Some proofs are correct.
Fewer are convincing.
Post a problem. An editor puts it on the board. Then the room argues — and the argument that persuades the most readers carries the mark.
On the board
7 openA complete proof is within reach of anyone who has met the definitions. A good place to post first.
The sum of the first n odd numbers is a square
Show that for every positive integer n, … This is the friendliest thing on the board, and it is here deliberately. It has a proof by induction, a proof by pairing, and a proof that is a pict…
Prove the Pythagorean theorem
Let triangle ABC have its right angle at C. Write a = BC, b = CA, and c = AB. Prove that … Something over four hundred proofs are on record, and that abundance is itself the interesting fact…
How the board works
One
A problem is proposed
Anyone can submit. It waits in review until an editor puts it on the board, so the board stays a short list of problems worth the room’s time.
Two
Proofs are posted
Write in plain language with LaTeX where it helps — $a^2+b^2=c^2$ inline, $$…$$ for a display line.
Three
The room weighs them
One vote per reader per proof. Votes measure persuasion, not correctness — a proof can be right and still not be the one that makes you see it.
Four
One is recognized
The proof holding the most votes carries the brass mark. It moves when the votes move.