My favorite explanation of IUT is buried deep on Mochizuki's website: <a href="http://www.kurims.kyoto-u.ac.jp/~motizuki/sokkuri-hausu-link-english.pdf" rel="nofollow">http://www.kurims.kyoto-u.ac.jp/~motizuki/sokkuri-hausu-link...</a>
And accompanying animations: 1) <a href="https://www.youtube.com/watch?v=4hJTm8pTV5A" rel="nofollow">https://www.youtube.com/watch?v=4hJTm8pTV5A</a>
2) <a href="http://www.kurims.kyoto-u.ac.jp/~motizuki/IUT-animation-Thm-A-washi.avi" rel="nofollow">http://www.kurims.kyoto-u.ac.jp/~motizuki/IUT-animation-Thm-...</a>