The Master Theorem

In case you have never heard about "the secret society of puzzle solvers" at The Master Theorem, then get ready to face about 50 of the most creative, challenging and original puzzles you can find on the web. Even though the website rarely has been updated in the last few years, it can offer tens of hours of problem solving to all newcomers. In order to sign up and explore everything TMT has to offer, you must first complete one of the numerous puzzles posted there. An easy one you can start with is "Old McDonald", which can be solved using this... SPOILER.